Forget not the voice of thine enemies - The voice of thine enemies clamoring for the destruction of thy people. Compare Psalms 137:7. The prayer is, that God would bring deserved chastisement upon them for their purposes and their aims against his people. It is not necessarily a prayer for vengeance; it is a prayer for just retribution.
The tumult of those that rise up against thee - Of those that make war on thee, and on thy people. The word ““tumult” here means clamor or shout - as the shout of battle. The reference is to the movement of a host pressing on to conquest, encouraging and exciting each other, and endeavoring to intimidate their enemies by the loud clamor of the war-cry. It is a description of what had occurred among the main events referred to in the psalm, when the enemy came in to lay waste the capital, and to spread desolation throughout the land.
Increaseth continually - Margin, as in Hebrew, “Ascendeth.” That is, it seems to go up; it is the swelling clamor of a great multitude of warriors intent on conquest. A cry or clamor thus seems to swell or rise on the air, and (as it were) to ascend to God. The prayer here is, that God would regard that cry, not in the sense that he would grant them the fulfillment of their wishes, but in the sense that he would recompense them as they deserved. It is in this sense that the clamors of the wicked ascend to heaven - in this sense that God will regard them, as if they were a prayer for just retribution.