To be pure, to remain pure, can only come at a price, the price of knowing God and of loving him enough to do his will. He will always give us the strength we need to keep purity as something beautiful for God. Purity is the fruit of prayer. If families pray together they will remain in unity and purity, and love each other as God loves each one of them. A pure heart is the carrier of God’s love, and where there is love, there is unity, joy, and peace.
Source: Sex, God, and Marriage