Here "you" refers to the people of Israel. The word "forgotten" does not mean they have no memory of God. It means they no longer obey him. Alternate translation: "For you no longer obey"
This compares God to a large rock which people could climb on to get away from their enemies or hide behind. Alternate translation: "have ignored God, who is like a rock that protects you" or "have ignored the one who protects you" (See: [[rc://en/ta/man/jit/figs-metaphor]])