God wills that married love be a joyous union. God also wills that married love be procreative. When our human reasoning and attendant selfishness intrude to attempt to thwart God's will, conjugal love and the marital union itself may be threatened. Either we trust God, or we trust ourselves. Either we accept His will, or we accept our will.
Marriage forms around the begetting and educating of children.
Because love creates we naturally desire children. Most Catholics marry and have children. Children are a gift from God. Love in marriage grows by depending upon the Providence of God in keeping open every conjugal act to the possibility of having children. Knowing that each conjugal act might initiate a life adds to the drama of expecting to have one.