Psalms 41:13 - Wesley's Explanatory Notes

Amen — Signifies an hearty assent and approbation, and withal an earnest desire of the thing, to which it is annexed. And as the psalms are divided into five books, so each of them is closed with this word; the first here: the second, Psalms 72:19, the third, Psalms 89:52, the fourth, Psalms 106:48, the last in the end of Psalms 150:6, the doubling of the word shews the fervency of his spirit, in this work of praising God.