Ibn Ezra

Verily thou art a God, etc. Then they will confess to God and say, It is true that thou art God who hid himself from the people in which He delighted, and now thou art the God of the Israelites, who helps them. Some say that אל נסתר = אל מסתתר invisible God, and explain the verse thus: God, though invisible, revealed himself for the sake of Israel. This explanation, however, is not supported by the rules of Hebrew grammar, מסתתר being Hithpael, and signifying who hid himself.