John Trapp on Psalms 41:13

Verſ. 13. Bleſſed be the Lord God of Iſrael] Thus he ſweetly ſhutteth up this firſt book of the Pſalmes (as ſome diſtinguiſh) with a patheticall doxology, redoubling his Amen, Fiat, Fiat, to ſhew his fervency, and moſt earneſt deſire that God ſhould be bleſſed by his whole Iſrael. This was the cuſtome of the Scribes to do, ſaith Kimchi, when they had finiſhed any book. The other four books of Pſalmes (as they are reckoned) end in like manner.

From everlaſting to everlaſting] i.e. From the beginning of the World, to the end of it; or, as the Chaldee hath it, from this World, unto the World to come.

Amen and Amen] So be it, and ſo it ſhall bee. Dictio eſt acclamationis, approbationis, & confirmationis. The Rabbines ſay, that our Amen in the cloſe of our prayers muſt not be firſt, haſty, but with conſideration, 1 Cor. 14.16. Secondly, nor maimed or defective; wee muſt ſtretch out our hearts after it, and be ſwallowed up in God. Thirdly, nor alone, or an Orphan; that is, without faith, love, and holy confidence. The ſpirits of the whole prayer are contracted into it, and ſo ſhould the ſpirit of him that prayeth.