Sex has been designed by God to bring oneness in our lives. The pleasure is a side issue. Even children can be considered in some way as a side issue. Actually, the sexual union is the part that makes it a marriage, not the ceremony in the church. They aren't really married until that point, all they've done is have a wedding ceremony.
Sexual intercourse is a covenant activity.
In it, the two parties entering into covenant cut themselves and mingled their blood. When a woman loses her virginity she bleeds. This blood goes onto the man's penis. The man is in her blood, with her flesh on either side of him, just as the parties entering into covenant. Each time that couple comes together again in sex, they are reenacting their covenant.