(Verse 11 onward) Upon this, my belly will sound like a lyre to Moab: and my bowels will be like a wall of baked bricks. And when it becomes clear that Moab has labored in vain, he will enter his sanctuaries to pray, but he will not prevail. This is the word that the Lord spoke to Moab from that time on. The error of Moab has been destroyed; indeed, false joy has turned into mourning and tears. My belly, the prophet, who is composed like a lyre with musical skill, and who, conceived in the fear of God, has produced many children, so that there is no string that does not produce its sound, will resonate the lament of Moab, who is repenting: and all my bowels will be like a wall of baked bricks, as Theodotius interpreted it as a wall scattered. For all the defenses of opposites, in which they previously trusted, will be destroyed and will fall. These, however, are the bowels and inner parts of the prophet, about which David also said in the Psalm: Bless the Lord, O my soul, and let all my innards proclaim his holy name (Psalm 102, 1). For just as a lyre does not emit a vocal sound and harmonious, if at least one string is broken; similarly, the spiritual belly of the prophet, if one string of virtues is lacking in it, will not be able to resound sweet melody; nor proclaim with all its innards against the brick wall. It is also the opinion of the philosophers to cling to virtues; and the Apostle James says that if one is lacking one virtue, all virtues are lacking in that person. But when he realizes that he has labored in vain in the lofty doctrines which he once believed, he will enter into his own holy things, not those things which are inherently holy, but those things which he erroneously thought were holy, and he will not be able to find help. Perhaps, in the desert of error and falsehood, he will attempt to enter into the holy Church, to make it his own, and to pray and beseech, but he will not prevail. For we cannot immediately, as we wish, attain perfect virtue. And this is what it means: That word which the Lord spoke to Moab from that time, with the introductory statement in which he said, the word against Moab, or the burden, let us understand it as the conclusion, so that what he began there, he may complete here. From that time, however, we should understand from when he began to speak to him, that everything he said is one word of God, that is, one sentence. Moreover, according to the Septuagint version, we can explain the prophet's innermost thoughts being renewed by God, and him being ashamed, that is, Moab, and entering into the altars, and the things that are made by hand, so that we may say that the prophet's innermost thoughts are always renewed, and made stronger by God, so that their adversaries may be confounded, and they may understand that the things made by human hand are useless, and do not contribute to salvation.
(Verse 13.) This is the word that the Lord spoke to Moab from that time. From when do you think? Obviously from the time that Moab was created. And the Lord says: The Moabites and Ammonites shall not enter into the Church of God (Deut. XXIII, 3). Whether we understand it from that time as referring to ancient times, which long ago this divine sentence was decreed, not that the foreknowledge of God brought about the cause of the devastation; but that the future devastation was foreknown to the majesty of God.
[AD 420] Jerome on Isaiah 16:11-13