John Calvin Commentary Psalms 41:13

"Blessed be Jehovah, the God of Israel, From everlasting and to everlasting. Amen, and Amen. Book II" — Psalms 41:13 (ASV)

Blessed be Jehovah, the God of Israel, for ever and ever. Here, the Psalmist confirms and repeats the expression of thanksgiving contained in a preceding verse. By calling God expressly the God of Israel, he testifies that he cherished in his heart a deep and thorough impression of the covenant which God had made with the Fathers, because it was the source from which his deliverance proceeded. The term amen is repeated twice to express the greater vehemence and so that all the godly might be more effectively stirred up to praise God.