Psalms 89:51 - Matthew Poole's English Annotations on the Holy Bible

Or, of thy Messiah; by whom he seems to understand either, first, the kings of Judah, the singular number being put for the plural; and by their footsteps may be meant either their ways or actions, and the sad consequences thereof; or the traces or memorials of their ancient splendour and dominion, wherewith they now upbraid them: or rather, secondly, the Messiah, most properly and eminently so called; of whom not only many Christians, but the Chaldee paraphrast and the Hebrew doctors, understand this place. And this suits very well, both with the singular number here used, which points at one particular and eminent person anointed by God to be the king of his people, and with the matter and occasion of this Psalm. For it was universally believed by the Jews, that the Messiah should come of the seed of David, and that by him the ancient glory and power of David's house should be revived and vastly increased. And this coming of the Messiah the Jews did continually expect for a long time together before he did come, and supported themselves therewith under all their calamities; all which being well known to many of the heathens, they reproached the Jews with the vanity of this belief and expectation. And by the footsteps of the Messiah he may understand his coming, as by the feet or footsteps of ministers, Isaiah 52:7, their coming and bringing the gospel with them is understood.