Albert Barnes Commentary Psalms 80:15

"And the stock which thy right hand planted, And the branch that thou madest strong for thyself." — Psalms 80:15 (ASV)

And the vineyard ... - Gesenius renders this as a verb: “Protect;” that is, “Protect or defend what your right hand has planted.” So the Septuagint renders it κατάρτισαι katartisai - and the Vulgate, perfice, fit, prepare, order. Prof. Alexander renders it sustain. DeWette, “Guard what your right hand has planted.” This is doubtless the true idea. It is a prayer that God would guard, sustain, defend what he had planted; namely, the vine which he had brought out of Egypt (Psalms 80:8).

And the branch - literally, the son; that is, the offspring or shoots of the vine. Not merely the original plant - the parent stock - but all the branches which had sprung from it and which had spread themselves over the land.

That thou madest strong for thyself - You caused it to grow so vigorously for your own use or honor. On that account, we now call on you to defend what is your own.