1 Judge me, O God, and plead my cause against an ungodly nation: O deliver me from the deceitful and unjust man. 2 For thou art the God of my strength: why dost thou cast me off? why go I mourning because of the oppression of the enemy? 3 O send out thy light and thy truth: let them lead me; let them bring me unto thy holy hill, and to thy tabernacles. 4 Then will I go unto the altar of God, unto God my exceeding joy: yea, upon the harp will I praise thee, O God my God. 5 Why art thou cast down, O my soul? and why art thou disquieted within me? hope in God: for I shall yet praise him, who is the health of my countenance, and my God.
[AD 430] Augustine of Hippo on Psalms 43:1
"Judge me, O Lord, and separate my cause from the ungodly nation" [Psalm 43:1]. I do not dread Your judgment, because I know Your mercy. "Judge me, O God," he cries. Now, meanwhile, in this state of pilgrimage, Thou dost not yet separate my place, because I am to live together with the "tares" even to the time of the "harvest:" Thou dost not as yet separate my rain from theirs; my light from theirs: "separate my cause." Let a difference be made between him who believes in You, and him who believes not in You. Our infirmity is the same; but our consciences not the same: our sufferings the same; but our longings not the same. "The desire of the ungodly shall perish," but as to the desire of the righteous, we might well doubt, if He were not "sure" who promised. The object of our desires is He Himself, who promises: He will give us Himself, because He has already given Himself to us; He will give Himself in His immortality to us then immortal, even because He gave Himself in His mortality to us when mortal....

[AD 430] Augustine of Hippo on Psalms 43:1
Some one, perchance, hears a person saying, “Judge me, O God,” and he is amazed. For one usually says, “May God pardon me; spare me, O God.” Who is there who says, “Judge me, O God”? And sometimes in the psalm this very verse is placed at a pause point, that it may be proffered by the reader and answered by the people. Is there perhaps anyone whose heart is not deeply affected and who is not afraid to sing to God and say, “Judge me, O God”? And yet the people sing it, believing, and do not think that they wrongly desire what they have learned from the divinely inspired text; and if they little understand.… For it continued and showed in the words coming next what kind of judgment it meant, that it is not [the judgment] of damnation but of discerning. For the psalm says, “Judge me, O God.” What does it mean, “Judge me, O God”? “And discern my cause from an unholy nation.” … According to that mode whereby judgment is called distinction, “All of us must be revealed before the judgment seat of Christ so that there” a person “may receive what he has done through the body, whether good or evil”; for it is distinction that good things be distributed to the good, evil things to the evil. For if judgment were received always in regard to evilness, the psalm would not say, “Judge me, O God.”

[AD 458] Theodoret of Cyrus on Psalms 43:1
The psalm is without a title in the Hebrew for the reason of having a similar meaning to the preceding one.

[AD 430] Augustine of Hippo on Psalms 43:2
And since patience is needful in order to endure, until the harvest, a certain distinction without separation, if we may so speak (for they are together with us, and therefore not yet separated; the tares however being still tares, and the grain still grain, and therefore they are already distinct); since then a kind of strength is needful, which must be implored of Him who bids us to be strong, and without whose making us strong, we should not be what He bids us to be; of Him who said, "He that endures unto the end shall be saved," [Matthew 24:31] lest the soul's powers should be impaired in consequence of her ascribing any strength to herself, he subjoins immediately, "For Thou, O God, art my strength: why have You cast me off, and why go I mourning, while the enemy harasses me?" [Psalm 43:2]. I go mourning: the enemy is harassing me with daily temptations: inspiring either some unlawful love, or some ungrounded cause of fear; and the soul that fights against both of them, though not taken prisoner by them, yet being in danger from them, is contracted with sorrow, and says unto God, "Why?" Let her then ask of Him, and hear "Why?" For she is in the Psalm enquiring the cause of her dejection; saying, "Why have You cast me off? And why go I mourning?" Let her hear from Isaiah; let the lesson which has just been read, suggest itself to her. "The spirit shall go forth from me, and every breath have I made. For iniquity have I a little afflicted him; I hid my face from him, and he departed from me sorrowful in the ways of his heart." [Isaiah 57:16-17] Why then did you ask, "Why have You cast me off, and why go I mourning?" You have heard, it was "for iniquity." "Iniquity" is the cause of your mourning; let "Righteousness" be the cause of your rejoicing! You would sin; and yet you would fain not suffer; so that it was too little for you to be yourself unrighteous, without also wishing Him to be unrighteous, in that you would fain not be punished by Him. Consider a speech of a better kind in another Psalm. "It is good for me that You have humbled me, that I might learn Your righteousnesses." By being lifted up, I had learned my own iniquities; let me by being "humbled," learn "Your righteousnesses." "Why go I mourning, while the enemy harasses me?" You complain of the enemy. It is true he does harass you; but it was you who "gave place" [Ephesians 4:27] to him. And even now there is a course open to you; choose the course of prudence; admit your King, shut the tyrant out.

[AD 390] Diodorus of Tarsus on Psalms 43:3
Dispatch your reliable assistance (by “light” referring to the support, and by “truth” to its reliability) … so that your reliable help may conduct me to the holy places and your holy temple.

[AD 399] Evagrius Ponticus on Psalms 43:3
The holy mount of God is Christ. His tabernacle indwells the virtues of the righteous.

[AD 430] Augustine of Hippo on Psalms 43:3
But in order that she may do this, hear what she says, what she supplicates, what she prays for. Pray thou for what you hear; pray for it when you hear it; let these words be the voice of us all: "O send out Your Light and Your Truth. They have led me, and brought me on unto Your holy hill, and into Your Tabernacles" [Psalm 43:3]. For that very "Light" and "Truth" are indeed two in name; the reality expressed is but One. For what else is the "Light" of God, except the "Truth" of God? Or what else is the "Truth" of God, except the "Light" of God? And the one Person of Christ is both of these. "I am the Light of the world: he that believes in Me, shall not walk in darkness." "I am the Way, the Truth, and the Life." He is Himself "the Light:" He is Himself "the Truth." Let Him come then and rescue us, and "separate at once our cause from the ungodly nation; let Him deliver us from the deceitful and unjust man," let him separate the wheat from the tares, for at the time of harvest He will Himself send His Angels, that they may "gather out of His kingdom all things that offend," [Matthew 13:41] and cast them into flaming fire, while they gather together the grain into the garner. He will send out His "Light," and His "Truth;" for that they have already "brought us and led us to His holy hill, and into His Tabernacles." We possess the "earnest;" we hope for the prize. "His holy Hill" is His holy Church. It is that mountain which, according to Daniel's vision, [Daniel 2:35] grew from a very small "stone," till it crushed the kingdoms of the earth; and grew to such a size, that it "filled the face of the earth." This is the "hill," from which he tells us that his prayer was heard, who says, "I cried unto the Lord with my voice, and He heard me out of His holy hill." Let no one of those that are without that mountain, hope to be heard unto eternal life. For many are heard in their prayers for many things. Let them not congratulate themselves on being heard; the devils were heard in their prayer, that they might be sent into the swine. Let us desire to be heard unto eternal life, by reason of our longing, through which we say, "Send out Your Light and Your Truth." [Matthew 8:31-32] That is a "Light" which requires the eye of the heart. For "Blessed" (He says) "are the pure in heart, for they shall see God." [Matthew 5:8] We are now on His Hill, that is, in His Church, and in His Tabernacle. The "tabernacle" is for persons sojourning; the house, for those dwelling in one community. The tabernacle is also for those who are both from home, and also in a state of warfare. When you hear of a tabernacle, form a notion of a war; guard against an enemy. But what shall the house be? "Blessed are they that dwell in Your house: they will be always praising You."

[AD 460] Arnobius the Younger on Psalms 43:3
Send your light and overcome my shadows. Send your truth and conquer my lying. Your light and truth lead me to your holy mountain and into your tabernacle. When I draw near, you lead me to the altar of God, where, although old, I become as a youth.

[AD 461] Leo the Great on Psalms 43:3
The beam that emanates from light does not come after the light. True light never lacks a beam, having it as part of its substance to shine, just as it always has it as part of its substance to exist. But the manifestation of this beam has been called a “sending,” by which Christ appeared to the world. Although he filled all things with his invisible majesty, he came, nevertheless, to those who had not known him, as if from a very remote and deep seclusion. At that time, he took away the blindness of ignorance, as it has been written: “For those sitting in darkness and in the shadow of death, a light has risen.” Of course the light of truth has been sent out in prior ages to enlighten the holy fathers and prophets, as when David said, “Send out your light and your truth.” Of course the divinity of the Son has made clear the works of his presence “in various ways and by many signs.” Yet all these prefigurations and all these miracles bore testimony about that “sending” of which the apostle speaks: “When the fullness of time came, God sent his Son, made from a woman, made under the Law.”

[AD 430] Augustine of Hippo on Psalms 43:4
Now then that we have been led on even to "the Tabernacle," and are placed on "His holy Hill," what hope do we carry with us? "Then will I go in unto the Altar of God" [Psalm 43:4]. For there is a certain invisible Altar on high, which the unrighteous man approaches not. To that Altar he alone draws near, who draws near to this one without cause to fear. There he shall find his Life, who in this one "separates his cause." "And I will go in unto the Altar of God." From His holy Hill, and from His Tabernacle, from His Holy Church, I will go in unto the Altar of God on High. What manner of Sacrifice is there? He himself who goes in is taken for a burnt-offering. "I will go in unto the Altar of God." What is the meaning of what he says, "The Altar of my God"? "Unto God, who makes glad my youth." Youth signifies newness: just as if he said, "Unto God, who makes glad my newness." It is He who makes glad my newness, who has filled my old estate with mourning. For now "I go mourning" in oldness, then shall "I stand," exulting in newness! "Yea, upon the harp will I praise You, O God my God." What is the meaning of "praising on the harp," and praising on the psaltery? For he does not always do so with the harp, nor always with the psaltery. These two instruments of the musicians have each a distinct meaning of their own, worthy of our consideration and notice. They are both borne in the hands, and played by the touch; and they stand for certain bodily works of ours. Both are good, if one knows how to play the psaltery, or to play the harp. But since the psaltery is that instrument which has the shell (i.e. that drum, that hollow piece of wood, by straining on which the chords resound) on the upper part of it, whereas the harp has that same concave sounding-board on the lower part, there is to be a distinction made between our works, when they are "upon the harp," when "on the psaltery:" both however are acceptable to God, and grateful to His ear. When we do anything according to God's Commandments, obeying His commands and hearkening to Him, that we may fulfil His injunctions, when we are active and not passive, it is the psaltery that is playing. For so also do the Angels: for they have nothing to suffer. But when we suffer anything of tribulation, of trials, of offenses on this earth (as we suffer only from the inferior part of ourselves; i.e. from the fact that we are mortal, that we owe somewhat of tribulation to our original cause, and also from the fact of our suffering much from those who are not "above"); this is "the harp." For there rises a sweet strain from that part of us which is "below:" we "suffer," and we strike the psaltery, or shall I rather say we sing and we strike the harp....

[AD 390] Diodorus of Tarsus on Psalms 43:5
I shall console myself and … not allow myself to be alarmed by my thoughts but to hope in you, my God, to whom I should also give thanks, for from you it is also possible to hope for salvation.

[AD 430] Augustine of Hippo on Psalms 43:5
And again, in order that he may draw the sound from that sounding-board below, he addresses his soul: he says, "Why are you sorrowful, O my soul, and why do you disquiet me?" [Psalm 43:5]. I am in tribulations, in weariness, in mourning, "Why do you disquiet me, O my soul?" Who is the speaker, to whom is he speaking? That it is the soul to which he is speaking, everybody knows: for it is obvious: the appeal is addressed to it directly: "Why are you sorrowful, O my soul, and why do you disquiet me?" The question is as to the speaker. It is not the flesh addressing the soul, surely, since the flesh cannot speak without the soul. For it is more appropriate for the soul to address the flesh, than for the flesh to address the soul....We perceive then that we have a certain part, in which is "the image of God;" viz. the mind and reason. It was that same mind that prayed for "God's Light" and "God's Truth." It is the same mind by which we apprehend right and wrong: it is by the same that we discern truth from falsehood. It is this same that we call "understanding;" which "understanding," indeed, is wanting to the brutes. And this "understanding" whoever neglects in himself, and holds it in less account than the other parts of his nature, and casts it off, just as if he had it not, is addressed in the Psalm, "Be not as the horse and the mule, which have no understanding." It is our "understanding" then that is addressing our soul. The latter is withered away from tribulations, worn out in anguish, made "sorrowful" in temptations, fainting in toils. The mind, catching a glimpse of Truth above, would fain rouse her spirits, and she says, "Why are you sorrowful, O my soul?"...

[AD 458] Theodoret of Cyrus on Psalms 43:5
From this it is clear that both psalms have the same meaning. Those using them encourage themselves to have stronger hope, overcome the feeling of discouragement and await the salvation from God that will doubtless be given them.