Keep in mind the concept of agency and autonomy. God is autonomous. He has freedom to choose. We have agency if we act in accordance to God's will. In other words God will delegate his autonomy to us if we obey him. However, God will not be beholden to us. If God makes a promise along the lines of "If you do this then I will do that" then God is placing control in our hands.
Okay... let's break this down. Romans 4:4 says that if God responds to works of man then God becomes a debtor to works of man. I.E. This elevates man above God, and that's a big no-no. Romans 4:5 clarifies that God grants his grace as he sees fit, placing God once more above man.