On the heights of Sinai, God gave the truth to Moses, in the Ten Commandments. These showed out the truth about the purpose of life, and about the relations between men and women. These truths can never change. No wise theologian contradicts them to say that God's will need not reign supreme, or that men and women can make their union sterile not fruitful.
What happens at Mass surpasses even those theophanies of the Old Testament times. God revealed Himself as fire in the burning bush, and on Mount Sinai, and in the desert, as Moses guided the chosen people. But we who are God's people today are privileged to have God Present with us: Jesus Christ, God-made-man, bodily Present, hidden under the form of bread and wine.
We learned that God's presence was experienced long ago amidst thunder and fire, on Sinai. People today who live in serious sin and are afraid of God, feel as though He is a God of terror and fire. All who have been purified in Baptism - or, later, in Reconciliation - can realise that God is love: a tender love, in which He enfolds those who trust in Him and strive to do His Will. Their souls are at peace.