John 12:36

Let us see what idea we are to form from the language of Paul regarding Christ where he says that he is the “brightness of the glory of God and the representation of his being.” According to John, “God is light.” The only-begotten Son, therefore, is the glory of this light, proceeding inseparably from God himself, just as brightness proceeds from light and illuminates the whole creation.… Through this brightness, human beings understand and experience what light itself is. And this splendor presents itself gently and softly to the frail and weak eyes of mortals and gradually trains and accustoms them, as it were, to bear the brightness of the light. It removes from them every hindrance and obstruction to their vision, according to the Lord’s own command to cast out the beam from your own eye. In this way, it renders them capable of enduring the splendor of the light and becomes, in this respect, also a kind of mediator between human beings and the light.

(Hom. lxviii. 1) Wherefore He adds, While ye have the light, believe in the light.

(Hom. lxviii) i. e. My children. In the beginning of the Gospel it is said, Born of God, (c. 1:13) i. e. of the Father. But here He Himself is the Begetter. The same act is the act both of Father and Son.
These things spake Jesus, and departed, and did hide Himself from them.

(Hom. lxviii. 1) But why did He hide Himself, when they neither took up stones to cast at Him, nor blasphemed? Because He saw into their hearts, and knew the fury they were in; and therefore did not wait till they broke out into act, but retired to give their envy time to subside.

"Walk in the light, that ye may become children of the light." That is, "My children." Yet in the beginning the Evangelist saith, "Were born, not of bloods, nor of the will of the flesh, but of God" (c. i. 13); that is, of the Father; while here Himself is said to beget them; that thou mayest understand that the operation of the Father and the Son is One. "Jesus having spoken these things," departed from them, and did hide Himself. Why doth He now "hide Himself"? They took not up stones against Him, nor did they blaspheme Him in any such manner as before; why then did He hide Himself? Walking in men's hearts, He knew that their wrath was fierce, though they said nothing; He knew it boiling and murderous, and waited not till it issued into action, but hid Himself, to allay their ill-will.

(Tr. lii) i. e. While ye have any truth, believe in the truth, that ye may be born again of the truth: That ye may be the children of the light.

(Tr. lii) Not from those which began to believe in and love Him, but from those who saw and envied Him. When He hid Himself, He consulted our weakness, He did not derogate from His own power.

"While ye have the light," He adds, "believe in the light, that ye may be the children of light." While you have possession of some truth that you have heard, believe in the truth, that you may be born again in the truth.

"These things spake Jesus, and departed, and did hide Himself from them." Not from those who had begun to believe and to love Him, nor from those who had come to meet Him with branches of palm trees and songs of praise; but from those who saw and hated Him, for they saw Him not, but only stumbled on that stone in their blindness. But when Jesus hid Himself from those who desired to slay Him, He had regard to our human weakness, but derogated not in aught from His own authority.

These things spake Jesus, and He departed and hid Himself from them.

After teaching them in few words what was profitable, once again by God-befitting power He betakes Himself from their midst, concealing Himself; and not permitting them to be roused to anger, but giving them opportunity to change their mind, with intent that they might do what was better. And He withdraws with a set purpose, His Passion being nigh; showing that it was not His will to be put to death by the Jews, notwithstanding that He willingly yielded Himself up to suffer, giving Himself a Ransom for our life; and accepted death, which men naturally liken unto sorrow, and changed the sorrow into gladness.

While ye have the Light, believe on the Light, that ye may become sons of Light.

He proved therefore that the faith which is in Him, through Whom a man comes to the knowledge also of the Father, is the way of salvation. And He names them sons of Light whether of Himself or of the Father, for He speaks of the Father as Light after having spoken of Himself as Light----in order to show that the Nature of Himself and of His Father is One: and we become sons of the Father, when, through the faith which is in Christ, we accept the Father Who is Light; for then shall we also be entitled children of God.

Jesus withdraws with a set purpose, his passion being close at hand, showing that it was not his will to be put to death by the Jews. Nevertheless, he willingly yielded himself up to suffer, giving himself as a ransom for our life and accepting death, which is cause for sadness. But he ends up changing sorrow into gladness.

So then, while the Light is with you, walk, that is, believe in Me. What time is He speaking of here? He speaks of the time before the sufferings, or of the time after the sufferings, or of both together. So then, He says, walk and believe in Me both before My crucifixion and after it. He indicates this by the words "while the Light is with you," that is, while you can believe in Me; and to believe in Me, who am the Light, you can both before the sufferings and after them. But whoever walks in unbelief does not know where he is going. For whatever the Jews do now, they nevertheless do not know what they are doing, but walk as if in darkness; they think they are going on the straight path, but everything turns out the opposite for them, when they observe the Sabbath and circumcision. But those who have believed do not act this way. They walk in the light, doing everything that pertains to salvation. For they escaped the shadows of the law and the darkness of riddles, and came to the light that had been hidden in them but has now shone forth, and became sons of the Light, that is, of Christ. "That you may become," He says, "sons of the Light," that is, My sons. Although the Evangelist at the beginning of the Gospel says that some were born of God (John 1:13), here he calls them sons of the Light, that is, of Christ. Let Arius and Eunomius be put to shame. For here too it is shown that the Father and the Son have one operation.
Why did the Lord hide from them? They had not now taken up stones against Him, nor spoken any blasphemy, as before. Why then did He hide? Although they said nothing, yet penetrating into their hearts, He saw that their fury was increasing. To subdue their hatred, He hides Himself.

Then when he says, While you have the light, believe in the light, he explains what he said, namely, what it means to walk. This is explained in two ways, according to the two explanations given above. According to the first explanation: While you have the light, that is, while you have some knowledge and light of the truth, believe in the light, that is, in the complete truth, that you may become sons of light, that is, that you may be reborn in the truth: "We are not of the night or of darkness. So then let us not sleep" (1 Thess 5:6).

Or, according to the other explanation: While you have the light, that is, me who am the light - "He was the true light which enlightens every man who comes into the world" (1:9) - believe in the light, that is, in me. In other words, make progress in the knowledge of me, that you may become sons of light, because from the fact that you believe in me you will be the children of God: "But to all who receive him, who believed in his name, he gave power to become children of God" (1:12).

When Jesus had said this, he departed and hid himself from them. Here the Evangelist tells what Jesus did, that he hid himself. When we read above (8:59) that Christ did this very thing, the reason was obvious, for they were taking stones to cast at him. But here there is no reason for his hiding given, such as that they took up stones or that they blasphemed him. Why then did he hide? The answer is that our Lord, seeing into their hearts, knew their rage and the evil they had planned, i.e., to kill him. And so in his desire to stop them he did not wait for them to act, but hid himself so their anger and envy would abate. In doing this he is an example to us that when the evil purposes of others are clear to us, we should flee before they can accomplish them. In addition, our Lord was showing by his actions what he had said by his words. For he just said, Walk while you have the light, lest the darkness overtake you. And by hiding himself he indicated what sort of darkness he means: "I will wait for the Lord, who is hiding his face from the house of Jacob" (Is 8:17).