John Calvin Commentary Isaiah 38:20

"Jehovah is [ready] to save me: Therefore we will sing my songs with stringed instruments All the days of our life in the house of Jehovah." — Isaiah 38:20 (ASV)

Jehovah to save me. He acknowledges that he was delivered, not by the help or efforts of men, but solely by the kindness of God. The rendering given by some, “It belongs to the Lord to save me,” does not express enough, and appears to be more remote from the literal meaning; for he praises not only the power of God, but also the work by which He has given an evident proof of it. In a word, he contrasts God’s keeping with the death to which he had been sentenced; because, having formerly dreaded Him as a severe judge, he now declares Him to be his deliverer, and leaps with joy.

And we will sing our songs. For the reason now stated, he not only prepares himself for singing as a sign of gratitude, but also calls on others to join and accompany him in this duty, and for this reason mentions the Temple, in which the assemblies of religious men were held. Had he been a private individual and one of the common people, still it would have been his duty to offer a public sacrifice to God, so that he might encourage others by his example. Much more then was the king bound to ensure that he brought others to unite with him in thanksgiving; especially because in his person God had provided for the advantage of the whole Church.

All the days of our life. He declares that he will make every effort so that this favor of God may be known to all, and that the remembrance of it may be preserved, not only for one day or for one year, but as long as he lives. And indeed, at any time it would have been exceedingly shameful to allow a blessing of God so remarkable as this to pass away or be forgotten; but, being forgetful, we continually need spurs to arouse us. At the same time, he briefly notes the reason why God appointed holy assemblies. It was so that all, as with one voice, might praise Him, and might encourage each other in the practice of godliness.