And men shall speak of the might of thy terrible acts - The force, the power of those things done by thee which are suited to inspire fear or reverence. The great power displayed in those acts shall be a ground or reason for celebrating thy praise. The manifestations of that power will so deeply impress the minds of people, that they will be led to speak of them.
And I will declare thy greatness - Hebrew, "And thy greatness, I will declare it." In respect to that, I will recount it, or I will make it known to others.

And [men] shall speak of the might of thy (d) terrible acts: and I will declare thy greatness.
(d) Of your terrible judgments against the wicked.

And men shall speak of the might of thy terrible acts,.... The terrible things of Christ, which his right hand has taught him, and his mighty power has performed; such as the destruction of a disobedient and ungodly world by a flood, to whom he preached by his Spirit in the days of Noah; the burning of Sodom and Gomorrah by raining on them fire and brimstone from the Lord out of heaven; and the dreadful things he did in Egypt and at the Red sea by the hands of Moses; these, men or saints of the former dispensation, in, before, and after the times of David, could speak of: there are others done by him on the cross, as the bruising the serpent's head, destroying his works, and him himself with his principalities and powers; and at the time of his sufferings, when the sun was darkened at noon day, the earth quaked, the rocks were split, the vail of the temple rent in twain, and graves opened, which threw the centurion and his soldiers into a panic that watched Jesus on the cross; and at his resurrection, when was a great earthquake also, and angels appeared, which made the keepers shake and tremble; and in a few years followed the terrible destruction of the Jewish nation, city, and temple, for the rejection of the Messiah; as also of Rome Pagan in a few ages after that; which are things besides the others that men under the Gospel dispensation can speak of: and there are others yet to be done, terrible to the kings of the earth, as the destruction of antichrist and all the antichristian states, the burning of Rome, the fall of the tenth part of the great city, or Romish jurisdiction, and also of the cities of the nations by an earthquake, and the downfall of all kingdoms and states, to make way for the everlasting kingdom of Christ. Now the power of Christ, as the mighty God, is seen in all these things, which show his eternal power and Godhead, and that with him is terrible majesty; and these are to be spoken of by good men to the terror of the wicked, and to command a proper awe and reverence of Christ in the minds of others;
and I will declare thy greatness; the greatness of his person, offices, and grace, as well as he could, being unsearchable; see Gill on Psalm 145:3.

terrible acts--which produce dread or fear.