At the other two angles were God and the devil. Luther like all humanity was caught between God and the devil. The devil tempts humanity to become like gods. Adam and Eve eat and their eyes are opened to good and evil and closed to God. The alliance is complete.
Most people today regard the devil as nothing more than a mythological creature.
I would say that the devil is nothing less than the product of our own vain imaginations. We in our resistance to God's mercy have created the Diabolical One so that we may form our own alliance against God. We do not want mercy. We want to be gods. But there is room for only one God in this triangle.