Blessed be Jehovah for ever! I am surprised why some interpreters should imagine, that this verse was added by some transcriber in copying the book, affirming, that it does not correspond with the context: as if the language of praise and thanksgiving to God were not as suitable at the close of a psalm as at the opening of it. I have therefore no doubt, that the prophet, after having freely bewailed the calamities of the Church, now, with the view of allaying the bitterness of his grief, purposely breaks forth into the language of praise. As to the words Amen, and Amen, I readily grant, that they are here employed to distinguish the book. [1] But whoever composed this psalm, there is no doubt, that by these words of rejoicing, the design of the writer was to assuage the greatness of his grief in the midst of his heavy afflictions, that he might entertain the livelier hope of deliverance.

Footnotes

1 - Or, as if our Redeemer were slow-paced, halt, or lame, and his Church should never behold his steps. With this agrees the Chaldee paraphrase: -- "The slowness of the footsteps of the feet of thy Messiah or anointed." Kimchi renders, "the delays of the Messiah;" "the discourse," he observes, "being of those who say that he will never come." A similar style of speech has been employed by the enemies of the gospel, as Calvin goes on to observe, who scoffingly asked in the days of the apostles, and who still ask, "Where is the promise of his coming?" 2-Peter 3:4.

Blessed be the Lord for evermore - Praise to God always. So Chrysostom was accustomed to say, even when driven out as an exile and a wanderer, "Blessed be God for everything." The passage here denotes entire acquiescence in God; perfect confidence in him; a belief that he was right, and faithful, and true. It is an instance of the faith which those who are truly pious have in God, in all circumstances, and at all times; of their belief that he is worthy of entire confidence, and ought always to be praised. Compare Job 1:21. At the close of all kinds of trouble - and in the midst of all kinds of trouble - true piety will enable us to say, "Blessed be God."

Blessed be the Lord for evermore - Let him treat us as he will, his name deserves eternal praises: our affliction, though great, is less than we have deserved.
This verse concludes the Third Book of the Psalter; and, I think, has been added by a later hand, in order to make this distinction, as every Masoretic Bible has something of this kind at the end of each book. The verse is wanting in one of Kennicott's and one of De Rossi's MSS.; in another it is written without points, to show that it does not belong to the text, and in three others it is written separately from the text. It is found, however, in all the ancient Versions. The Chaldee finishes thus: "Blessed be the name of the Lord in this world. Amen and Amen. Blessed be the name of the Lord in the world to come. Amen and Amen." And the reader will find no difficulty to subscribe his Amen, so be it.

Blessed be the Lord for evermore,.... In this world, and in the world to come, as the Targum; for reproaches and afflictions for Christ's sake, since they work together for good; as Job blessed the Lord in the midst of his troubles, Job 1:21, or rather the psalmist, viewing, by a spirit of prophecy, Christ rising from the dead, ascending to heaven, sitting at the right hand of God, and interceding for the application of all the blessings of the covenant; and now, seeing all before objected and complained of was reconcilable to the love, covenant, and oath of God, breaks out into this benediction, and with it closes the psalm; which agrees with Christ, not only as God over all, blessed for ever, but as Mediator, who, as such, is made most blessed for evermore; see Psalm 21:6. These are not the words of the copier of the Psalm, blessing God for assistance in prosecuting the work thus far, which is the sense of some Jewish writers mentioned by Aben Ezra and Kimchi, but of the psalmist himself:
Amen, and Amen; which words are added to express the wish and faith of the psalmist; and the word is repeated to denote the vehemence and strength of the same. Here ends the third part of the book of Psalm, and so the Syriac version closes it. See Gill on Psalm 41:13. See Gill on Psalm 72:20.

Blessed, &c.--denotes returning confidence (Psalm 34:1-3).
Amen, and Amen--closes the third book of Psalm.

(Hebrews.: 89:53) The closing doxology of the Third Book.

Blessed - Let thine enemies reproach thee and thy promises concerning the sending of the Messiah, I will heartily bless and praise thee for them, and encourage myself with them.