Verse 1-2
Isaiah 12:1-2. And, &c. — “Isaiah concludes this most noble prophecy with a doxology from the mouth of those who should share in the blessings of the great redemption before specified. This doxology is two-fold: in the first part, the redeemed, in their own names and persons, praise God for the benefits of salvation and consolation through Christ, conferred upon them. In the second part they mutually exhort and encourage themselves and others, to praise and celebrate their God and Redeemer.” Dodd. In that day — When this great work of the reduction of Israel, and the conversion of the Gentiles, promised in the foregoing chapter, is fulfilled: when the kingdom of the Messiah is set up in the world, in despite of all opposition from earth and hell; thou shalt say — Thou church of God, composed of Jews and Gentiles, united in one body, shalt say, as one man, with one mind and one mouth; and every particular member of the community shall say; that is, shall have cause to say, and a heart to say, O Lord, I will praise thee — “I will give thanks unto thee, O Jehovah;” so Bishop Lowth. For though thou hast been angry with me — Namely, while I was in my unenlightened and unconverted state of heathenish ignorance, or of Jewish unbelief; my state of sin and guilt, of depravity and alienation from thee; thine anger is turned away — In consequence of my conversion to thee by true repentance, unfeigned faith, and new obedience; and thou comfortedst me — By evident tokens of thy presence, communications of thy grace, and prospects of thy glory. Behold, God is my salvation — The author, giver, and source of my salvation; which, in all its branches and degrees, hath been effected, not by the power of man, but by the mercy and grace of God. He, therefore, shall have the glory of the salvation that has already been wrought for me, and from him only will I expect the salvation which I further need. And for this, I will trust — In his power, love, and faithfulness; and not be afraid — Lest he should deceive my confidence or disappoint my expectations; lest he should be either unable or unwilling to save me in time to come, as he has saved me in time past. For, not a dead idol, or a mere creature, whether made by man or God. but the Lord Jehovah — Hebrew, Jah Jehovah, (the former word being a contraction of the latter, and both signifying his self-existence, his eternity, and unchangeableness,) is my strength and my song — He, who is the living and true God, and who has all possible perfections in and of himself; he, who is both infinite and everlasting, hath undertaken my cause, and gives me both support in weakness and comfort in trouble; he enables me both to withstand my enemies and to rejoice and glory in him, being, as I know by experience, already become my salvation.

Verse 3
Isaiah 12:3. Therefore — Because the Lord Jehovah is your strength and song, and is, and will be, your salvation; with joy shall ye draw water, &c. — The assurances God has given you of his love, and the experience you have had of the benefit and comfort of his grace, should greatly encourage your faith in him, and your expectations from him. Out of the wells of salvation — Your thirsty and fainting souls shall be filled with divine graces and comforts; which you shall plentifully draw from God, in the use of gospel ordinances, and which are often signified by water, both in the Old and in the New Testament. He seems to allude to the state of Israel in the wilderness, where, when they had been tormented with thirst, they were greatly refreshed and delighted with those waters which God so graciously and wonderfully afforded them in that dry and barren land, Numbers 20:11; Numbers 21:16-18. As this hymn evidently appears by its whole tenor, and by many expressions in it, to be much better calculated for the Christian Church than it could be for the Jewish, in any circumstances, or at any time that can be assigned; so “the Jews themselves seem to have applied it to the times of the Messiah. On the last day of the feast of tabernacles, they fetched water, in a golden pitcher, from the fountain of Siloah, springing at the foot of mount Sion, without the city; they brought it through the water-gate into the temple, and poured it, mixed with wine, on the sacrifice as it lay upon the altar, with great rejoicing. They seem to have taken up this custom, for it is not ordained in the law of Moses, as an emblem of future blessings, in allusion to this passage of Isaiah: Ye shall draw water with joy from the fountains of salvation: expressions that can hardly be understood of any benefits afforded by the Mosaic dispensation. Our Saviour applied the ceremony, and the intention of it, to himself, and to the effusion of the Holy Spirit, promised and to be given by him.” Thus Bishop Lowth, who quotes a passage from the Jerusalem Talmud to show that the Jews thought this song to be intended of the times of the Messiah, and considered the water, said to be drawn from the wells of salvation, as signifying the influences of the Holy Spirit to be given in his days.

Verses 4-6
Isaiah 12:4-6. In that day ye shall say, &c. — Here we have the second part of the evangelical song, the subject of which, as of the former, is the praise of God. In the former part, believers stir up themselves to praise God; here they invite and encourage one another to do it, and are represented as contriving to spread his praise, and to draw in others to join with them in it. Praise the Lord, call upon his name — As giving thanks for former mercies is a modest way of begging for further mercies, so requesting further and fresh mercies is graciously accepted as a thankful acknowledgment of the mercies we have received. Declare, &c. — By speaking and writing. We must not only speak to God, but speak to others concerning him; not only call upon his name, but (as the margin reads it) proclaim his name. Let others know something more from us than they did before concerning God, and those things whereby he hath made himself known. His doings — Or, mighty deeds; as Bishop Lowth renders עלילתיו. The works of redemption and salvation are especially intended; these and his other wonderful works we should declare; among the people — Among the heathen, that they may be brought into communion with Israel, and the God of Israel. When the apostles preached the gospel to all nations, beginning at Jerusalem, then this scripture was fulfilled. Make mention — Hebrew, הזכירו, Record, or cause it to be remembered, that his name is exalted — Is become more illustrious and conspicuous than ever, in and by the incarnation and life, doctrine and miracles, death, and resurrection, and ascension of his Son, and the effusion of his Spirit, in gifts and graces, on the Messiah’s disciples and servants. Sing unto the Lord; for he hath done excellent things — For his people, to whom he hath given a wonderful proof of his love, and whom he hath magnified and made honourable. Bishop Lowth renders the original expression, שׁאית עשׁה, he hath wrought a stupendous work. In making his Son a sacrifice for our sins. This is known — Or, shall be made known; in all the earth — The knowledge of this glorious work shall no longer be confined to the land of Israel and Judah, as hitherto it hath been, but shall be published to all nations. Cry out and shout — In a holy exultation and transport of joy; thou inhabitant of Zion — Hebrew, שׁבת, inhabitress, thou daughter of Jerusalem, thou church of the living God, represented under the emblem of a woman. Welcome the gospel to thyself, and publish it to others with loud acclamations; for great is the Holy One of Israel in the midst of thee — Manifesting himself to thee, appearing and doing wonders for thee, and enriching thee with his gifts and graces in great abundance.