Adam Clarke on Ephesians 5:32

This is a great mystery - Το μυστηριον τουτο μεγα εστιν· This mystery is great. Sacramentum hoc magnum est; this sacrament is great. - Vulgate. And on the evidence of this version the Church of Rome has made matrimony a sacrament, which, as they use it, is no meaning of the original. By mystery, here, we may understand a natural thing by which some spiritual matter is signified, which signification the Spirit of God alone can give. So, here, the creation and union of Adam and Eve, were intended, in the design of God, to point out the union of Christ and the Church: a union the most important that can be conceived; and therefore the apostle calls it a great mystery. See the observations at the end of this chapter, (Eph 5:33 (note)).