Thou art my King, O God - literally, “Thou art He, my King, O God;” that is, Thou art the same: the same King, and the same God, who didst interpose in the time of the fathers, and thou art he whom I recognize as King, as the Sovereign Ruler of thy people. The psalmist here uses the singular number, “my King,” as expressive of his own feelings, though he doubtless means also to speak in the name of the people. It would seem not improbable from this, that the author of the psalm was the reigning monarch in the time of the troubles referred to. If not, it was evidently one who personated him, and who meant to represent his feelings. The language shows the strong confidence of the author of the psalm in God, and perhaps also is designed to express his personal responsibility at the time, and his consciousness that his only refuge in conducting the troubled affairs of the nation was God.
Command deliverances for Jacob - As if all was under His command, and He had only to give direction, and salvation would come. The word “Jacob” here is used to denote the descendants of Jacob, or the people of God. See the notes at Psalms 24:6.