For who is God save the Lord? - Who is God except Yahweh? The idea is, that no other being has evinced the power, the wisdom, and the goodness which properly belong to the true God; or, that the things which are implied in the true nature of God are found in no other being.
Or who is a rock save our God? - See Psalms 18:2. There is no one who can furnish such safety or defense; no one under whose protection we can be secure in danger. Compare Deuteronomy 32:31.