“Without some objective reference point we have no way of really saying if something is up or down.” On earth, the ground is always bellow us, so we can calibrate what everything else is in relation to it. In the same way God is our objective reference point for all of morality. Nothing else is as constant and consistent as him. Some people judge their morality in relation to the culture, but culture is always changing. God is always the same. Everything must be held up to him. This comes from apologist William Lane Craig’s video summarizing the moral argument for the existence of God: Watch Video