Christians follow Christ, but Christ is followed as either
a.) God made manifest as man in this present age.
b.) God manifesting man as he will exist in the eschaton.
According to (a), we are given sacraments. According to (b) we have the threefold vows of poverty, chastity, and obedience. By poverty, we participate in the common ownership of all goods in the eschaton; by celibacy we participate in final transcendence of eros; by obedience we live as if under the kingship of Christ.
Marriage is therefore a perfect sacramentum (Eph. 5:32) so far as it is a sign giving grace through a love fixed in this world. All other sacraments either give a permanent character and so are not fixed in this world (baptism, confirmation, orders – and its proper operation in eucharist) or are recognitions of the absence of perfection in body or soul (penance, anointing). Marriage alone lacks the permanent character and so is firmly situated in the world while elevating and recognizing the love and perfection in that world.