The vineyard which thy right hand hath planted - Thy holy and pure worship which thy Almighty power had established in this city.
And the branch - thou madest strong for thy self - The original בן ועל veal ben, "and upon the Son whom thou hast strengthened for thyself." Many have thought that the Lord Jesus is meant. And so the Chaldee understood it, as it translates the passage thus: משיחא מלכא ועל veal Malca Meshicha, And upon the King Messiah, whom thou hast strengthened for thyself." The Syriac, Vulgate, Septuagint, Ethiopic, and Arabic, have, "the Son of man,' as in the seventeenth verse. Eighteen of Kennicott's and De Rossi's MSS. have אדם בן ben Adam, "Son of man," and as the Versions have all the same reading, it was probably that of the original copies. As Christ seems here to be intended, this is the first place in the Old Testament where the title Son of man is applied to him. The old Psalter understands this of setting Christ at the right hand of God.
And the vineyard - Gesenius renders this as a verb: “Protect;” that is, “Protect or defend what thy right hand hath planted.” So the Septuagint renders it κατάρτισαι katartisai - and the Vulgate, perfice, fit, prepare, order. Prof. Alexander renders it sustain. DeWette, “Guard what thy right hand hath planted.” This is doubtless the true idea. It is a prayer that God would guard, sustain, defend what he had planted; to wit, the vine which he had brought out of Egypt, Psalm 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 - Thou didst cause it to grow so vigorously for thine own use or honor. On that account, we now call on thee to defend what is thine own.