Through God - By the help of God.
We shall do valiantly - literally, we shall make strength. That is, we shall gain or gather strength; we shall go forth with spirit and with courage to the war. This expresses the confident assurance that they would secure the aid of God, and that under him they would achieve the victory.
For he it is that shall tread down our enemies - He will himself tread or trample them down; that is, he will enable us to do it. The psalm, therefore, though begun in despondency and sadness, closes, as the Psalms often do, with confident hope; with the assurance of the favor of God; and with the firm belief that the object sought in the psalm would be obtained. The history shows that the prayer was answered; that the armies of David were successful; that Edom was subdued; and that thus the territories of the Hebrew people had, in fact, in the time of David, the boundaries promised to Abraham.