And thou shalt say in that day. Isaiah now exhorts all the godly to thanksgiving. Yet the exhortation has also this object, that the promise may be more fully believed; for he seals it with that exhortation, that they may be convinced that it is certain, and may not think that they are deluded by unfounded hope, when a form of thanksgiving is now given, and, as it were, put into their mouth; and this would not have been the case, if there had not been just and solid grounds. At the same time, he points out the purpose which the Lord has in view in doing good in his Church. It is, that the remembrance of his name may be extolled; not that he needs our praise, but it is profitable to ourselves. We ought also to consider the honor which he bestows upon us, when he condescends to make use of our services for extolling and spreading the glory of his name, though we are altogether useless and of no value. Thou shalt say. He addresses the whole people as if he were addressing one man, because it was their duty to be so united as to be one. We also are taught by the same example that we ought to be united together, that there may be one soul and one mouth, (Romans 15:6,) if we desire to have our prayers and thanksgivings accepted by God. Though thou wast angry with me. The leading thought of this song is, that God, though he was justly offended at his people, yet was satisfied with inflicting a moderate chastisement, and showed that he was willing to be pacified. The particle ky (ki) being sometimes expressive of a cause, some render it, I will praise thee, O Lord, because, having been angry with me, still thou art immediately reconciled; but as it sometimes signifies though, [1] I have adopted the rendering which I considered to agree best with this passage. Believers, therefore, first acknowledge their guilt, and next ascribe it to the mercy of God that they have been freed from their distresses. The words being in the future tense, the following interpretation might also be adopted: -- "The temporal chastisement will not prevent thee from having at length compassion on me, and from giving me ground of joy and comfort." Whichsoever of these views be taken, this sentiment ought to be carefully observed; for as soon as a conviction of God's anger seizes our minds, it prompts us to despair, and if it be not seasonably counteracted, it will speedily overwhelm us. Satan also tempts us by all methods, and employs every expedient to compel us to despair. We ought, therefore, to be fortified by this doctrine, that, though we feel the anger of the Lord, we may know that it is of short duration, (Psalm 30:5,) and that we shall be comforted as soon as he has chastened us. When we have been relieved from distresses, let us call to remembrance that our punishment is ended, not because we have paid to the justice of God what we had deserved, but because through his fatherly love he spares our weakness. This confession belongs properly to the godly and elect; for though the chastisements of the godly and ungodly appear to be the same, yet the reasons of them are exceedingly different. The wrath of the Lord against the ungodly is perpetual, and the chastisements which are inflicted on them are forerunners of everlasting destruction: no alleviation or consolation is promised to them. But the godly feel that the wrath of God is of short duration, and encourage their hearts by hope and confidence; for they know that God will be gracious to them, since he has declared that he punishes their sins for no other reason than to train them to repentance, that they may not perish along with the world. (1-Corinthians 11:32.)

Footnotes

1 - Lowth remarks that the Hebrew phrase is exactly the same with what we find in Romans 6:17. But thanks be to God that ye were the slaves of sin, but have obeyed from the heart; that is, that whereas, or though ye were the slaves of sin; yet ye have now obeyed from the heart the doctrine on the model of which ye were formed. "For thou wast angry. That is, whereas thou wast angry, now hast thou forgiven and comforted me." -- Stock.

And in that day - The day referred to in the previous chapter, the time of the Messiah, when the effects of his reign shall be seen everywhere. The duty of praise, however, is couched in such language as to make it applicable to the event predicted in the former part of the prophecy Isaiah. 10 - the delivering of the nation from the invasion of Sennacherib, as well as the more glorious event on which the prophet fixed his eye Isaiah. 11 - the coming and reign of the Messiah. The language of this song of praise would be appropriate to both these events.
Thou shalt say - The address to an individual here, in the term 'thou,' is equivalent to "everyone," meaning that "all" who were thus interested in the divine interposition should say it.
O Lord - O Yahweh - the great author of this interposition.
I will praise thee: though thou wast angry with me - If this language is applied to the Jews, and supposed to be used by them in regard to the invasion of Sennacherib, it means, that God suffered their land to be invaded, and to be subjected to calamities, in consequence of their sins (Isaiah 10:6 ff.) If it is supposed to be applied to the time of the Messiah, then it is language which every redeemed sinner may use, that God was angry with him, but that his anger is turned away. As applicable to the redeemed, it is an acknowledgement which they all feel, that they have no claim to his mercy, and that it lays the foundation for unceasing praise that his anger is turned away by the plan of salvation.

Though thou wast angry "For though thou hast been angry" - The Hebrew phrase, to which the Septuagint and Vulgate have too closely adhered, is exactly the same with that of St. Paul, Romans 6:17 : "But thanks be to God, that ye were the slaves of sin; but have obeyed from the heart;" that is, "that whereas, or though, ye were the slaves of sin, yet ye have now obeyed from the heart the doctrine on the model of which ye were formed."

And in that day thou (a) shalt say, O LORD, I will praise thee: though thou wast angry with me, thy anger is turned away, and thou didst comfort me.
(a) He shows how the Church will praise God, when they are delivered from their captivity.

And in that day thou shalt say,.... The following song of praise; just as Israel did, when they were brought through the Red sea, and saved out of the hands of their enemies; to which there are several allusions and references in it; that deliverance being typical of salvation by Christ; the Gospel day, or the times of the Gospel, are here meant:
O Lord, I will praise thee; or "confess thee"; to be my Lord, Redeemer, and Saviour, my Husband, Head, and King; or "confess to thee" (q), my sins and transgressions, and unworthiness to receive any favour from thee, and gratefully acknowledge all the favours bestowed upon me:
though thou wast angry with me; as it appeared to the church, and according to her apprehensions of things, though not in reality, or strictly or properly speaking; for anger is not to be ascribed to God; but it is a speaking after the manner of men; and the Lord seems to be angry when he hides his face from his people, when he refuses to hear their cries, when he afflicts them, and continues his hand upon them, and when he lets in a sense of wrath into their consciences:
thine anger is turned away; he granting his gracious presence; taking off his afflicting hand; manifesting his love, particularly his pardoning grace and mercy; peace and reconciliation being made by the blood of Christ, and justice satisfied, the effects of resentment and displeasure cease:
and thou comfortedst me; by shedding abroad his love in her heart; by discovering the free and full forgiveness of sin; by lifting up the light of his countenance; by an application of precious promises; and by means of the word and ordinances, through the influence of the blessed Spirit as a comforter; who leads in this way for comfort to the person, blood, righteousness, sacrifice, and fulness of Christ, and comforts with these, by applying them, and showing interest in them. The Targum is,
"and thou shalt say at that time, I will confess before the Lord; for that I have sinned before thee, thine anger is upon me; but when I am turned to the law, thine anger will turn from me, and thou wilt have mercy on me;''
or rather turned to Christ, and embrace his Gospel, which is the only way to have comfort.
(q) "confitebor tibi", V. L. Pagninus, Montanus.

The song of praise in this chapter is suitable for the return of the outcasts of Israel from their long captivity, but it is especially suitable to the case of a sinner, when he first finds peace and joy in believing; to that of a believer, when his peace is renewed after corrections for backslidings; and to that of the whole company of the redeemed, when they meet before the throne of God in heaven. The promise is sure, and the blessings contained in it are very rich; and the benefits enjoyed through Jesus Christ, call for the most enlarged thanksgivings. By Jesus Christ, the Root of Jesse, the Divine anger against mankind was turned away, for he is our Peace. Those to whom God is reconciled, he comforts. They are taught to triumph in God and their interest in him. I will trust him to prepare me for his salvation, and preserve me to it. I will trust him with all my concerns, not doubting but he will make all to work for good. Faith in God is a sovereign remedy against tormenting fears. Many Christians have God for their strength, who have him not for their song; they walk in darkness: but those who have God for their strength ought to make him their song; that is, give him the glory of it, and take to themselves the comfort of it. This salvation is from the love of God the Father, it comes to us through God the Son, it is applied by the new-creating power of God the Spirit. When this is seen by faith, the trembling sinner learns to hope in God, and is delivered from fear. The purifying and sanctifying influences of the Holy Ghost often are denoted under the emblem of springing water. This work flows through the mediation of Christ, and is conveyed to our souls by means of God's ordinances. Blessed be God, we have wells of salvation opened on every side, and may draw from them the waters of life and consolation. In the second part of this gospel song, ver. Isaiah 12:4-6, believers encourage one another to praise God, and seek to draw others to join them in it. No difference of opinions about the times and seasons, and other such matters, ought to divide the hearts of Christians. Let it be our care that we may be placed amongst those to whom he will say, Come, ye blessed of my Father, receive the kingdom prepared for you from the beginning of the world.

As Israel, when redeemed from Egypt beyond the Red Sea, sang songs of praise, so also will the Israel of the second redemption, when brought, in a no less miraculous manner, across the Red Sea and the Euphrates. "And in that day thou wilt say, I thank Thee, O Jehovah, that Thou wast angry with me: Thine anger is turned away, and Thou hast comforted me. Behold, the God of my salvation; I trust, and am not afraid: for Jah Jehovah is my pride and song, and He became my salvation." The words are addressed to the people of the future in the people of the prophet's own time. They give thanks for the wrath experienced, inasmuch as it was followed by all the richer consolation. The formation of the sentence after כּי is paratactic; the principal tone falls upon 1b, where yâshōb is written poetically for vayyâshob (cf., Deuteronomy 32:8, Deuteronomy 32:18; Psalm 18:12; Hosea 6:1). We hear the notes of Psalm 90:13; Psalm 27:1, resounding here; whilst Isaiah 12:2 is the echo of Exodus 15:2 (on which Psalm 118:14 is also founded). עזי (to be read ‛ozzi, and therefore also written עזי) is another form of עזּי, and is used here to signify the proud self-consciousness associated with the possession of power: pride, and the expression of it, viz., boasting. Zimrath is equivalent in sense, and probably also in form, to zimrâti, just as in Syriac zemori (my song) is regularly pronounced zemōr, with the i of the suffix dropped (see Hupfeld on Psalm 16:6). It is also possible, however, that it may be only an expansion of the primary form zimrath = zimrâh, and therefore that zimrath is only synonymous with zimrâti, as chēphetz in 2-Samuel 23:5 is with chephtzi. One thing peculiar to this echo of Exodus 15:2 is the doubling of the Jah in Jâh Jehōvâh, which answers to the surpassing of the type by the antitype.

In that day - When this great work of the reduction of Israel, and conversion of the Gentiles is fulfilled.