Cardinal Donald Wuerl (Bishop of part of Maryland explains)
"Marriage is a private relationship with a public significance. In the human love that brings a woman and a man to marriage, we already hear God speaking to us of the beauty and fidelity of love, its transforming power, and its creative energy. In the sacrament of matrimony, God speaks to us of a fullness of human love. Our limited experience of love is only a sign and beginning of love that changes us into children of God, who share his own wondrous and unending life in love."
Read the rest here.