Possible meanings are 1) Asaph is speaking as Israel's representative, "God has been our king since we Israelites first became a nation" or 2) "God, my king, was alive even in ancient times."
The abstract noun "salvation" can be translated with the verb "to save." Here Yahweh saving people is spoken of as if salvation were an object that he brings with him. Alternate translation: "saving people" (See: [[rc://en/ta/man/translate/figs-abstractnouns]] and [[rc://en/ta/man/translate/figs-metaphor]])