Then, i.e. of old; for this particle is sometimes put indefinitely. Or, then, when thou didst set David in the throne. In vision; which then was the usual way by which God spake to the prophets, Numbers 12:6. To thy holy one: to thy holy prophets; the singular number being put for the plural; especially to Samuel and Nathan; for part of the following message was delivered to the former, and part to the latter. I have laid help; I have provided help and relief for my people, which I have put into safe hands. Upon one that is mighty; upon a person of singular courage and wisdom, and every way fit for so great a charge. One chosen out of the people; one whom I have picked and chosen out of all the people, as the fittest for the kingly office, one enriched with eminent gifts and graces, &c.
Related Commentaries of Psalms 89:19
Psalms 89:19
19 Then thou spakest in vision to thy holy one, and saidst, I have laid help upon one that is mighty; I have exalted one chosen out of the people.