John Calvin Commentary Isaiah 12:5

"Sing unto Jehovah; for he hath done excellent things: let this be known in all the earth." — Isaiah 12:5 (ASV)

Sing to the Lord. He continues his exhortation, showing what is the feeling from which this thanksgiving should proceed; for he shows that it is our duty to proclaim the goodness of God to every nation. While we exhort and encourage others, we must not at the same time sit down in indolence, but it is proper that we set an example before others; for nothing can be more absurd than to see lazy and slothful men who are urging other men to praise God.

For he has done glorious things. When he asserts that God has done gloriously, he means that there is abundant ground for singing. The Lord does not wish that his praises should be proclaimed without any reason, but holds out a very rich and very abundant subject of praise, when he frees his people from very hard bondage. We have said that this song is not limited to a short period, but, on the contrary, extends to the whole of Christ’s reign. This work therefore is truly glorious, that God sent his Son to reconcile us to himself (John 3:16, 17) and to destroy the dominion of death and the devil (Hebrews 2:14). If, therefore, we consider the work of our deliverance as we should, we will have very abundant ground for praising God.

And this has been made known through all the earth. When he says that this has been made known, he alludes to the calling of the Gentiles, and confirms what has already been stated: that the work is such as should not be concealed in a corner, but should be proclaimed everywhere.