I believe that the Sacraments, or, as the Eastern Orthodox Christians would put them, the Sacred Mysteries, genuinely communicate God, the Most Sacred and the Grand Mystery himself. In particular, they gave us a glimpse of God’s climactic communication of himself in and through the redemptive work of Jesus of Nazareth. In that sense baptism and eucharist didn’t merely re-tell the story of Jesus, but invited us to be taken up in those stories as well. We become participants in that story and not only spectators.
Marriage, in some sense, also communicates the redemptive work of Jesus. Indeed, the husband-wife relationship is a metaphor of the YHWH-Israel and Christ-church relationship. You could feel some sense of holiness and mystery in a wedding ceremony. God’s enduring faithfulness to his people is symbolized by the lifelong commitment of the husband and the wife. Hence you could appreciate why the Roman Catholic and Eastern Orthodox churches put marriage as one of the sacraments/sacred mysteries. Their reasonings are valid enough for me.
But then in the end I would not accord marriage of the sacramental status, basically because marriage is not applicable for all. Unlike baptism and eucharist, which do are applicable for all. And I believe universality is one of the necessary litmus tests of what we call a sacrament, since a sacrament does not only communicates God, but also the whole people of God. Universality, of course, is what make baptism decisively different from circumcision. While, on the other hand, to use my previous metaphor, not all of us would be participants in a marriage.