Now also, when I am old and grayheaded, O God, forsake me not,.... A repetition of his request, Ps 71:9; with a reason annexed to it, suggested in the following words:until I have showed thy strength unto [this] generation; or, "thine arm" ; which sometimes the Messiah, Isa 53:1; who is the power of by whom he made the worlds, and in whom all things consist; and who has wrought out the salvation people; and is the arm on which they lean, and they are upheld.
And the psalmist may be thought to desire that he might be continued a little longer, and be favoured with the presence of God, and the influences of his Spirit and grace; that he might show forth in prophecy, both by word and writing, to the men of the then present age, more things concerning the person, office, and grace of Christ; his sufferings, death, resurrection from the dead, and session at the right hand of God; things which are spoken of in the book of Psalms.
Sometimes the arm of the Lord denotes his power and strength, Ps 44:3; and so it may be taken here; and the next clause seems to be an explanation of it:[and] thy power; or "[even] thy power",to everyone [that] is to come; that is, to come into the world, that is to be born into it; namely, the power of God, not only in creating all things out of nothing, and supporting what is made; but in the redemption of men, in the conversion of sinners, and in the preservation of the saints, and in enabling them to hold on and out unto the end: and which is shown forth by the psalmist in what he has committed to writing; and which continue, and will continue, to the end of the world, for the instruction of those that come into it; see Ps 22:31.
Kewrz "brachium tuum", V. L.