What is this law of God?

“God is not accountable to any laws outside of Himself. There are no independent, cosmic rules that God is obligated to obey. Rather, God is a law unto Himself. This simply means that God acts according to His own moral character. His own character is not only morally perfect, it is the ultimate standard of perfection. His actions are perfect because His nature is perfect, and He always acts according to His nature. God is therefore never arbitrary, whimsical, or capricious. He always does what is right.”- Essential Truths R.C. Sproul