I don't think that Paul is talking about marriage between a man and a woman as a "mystery". He has just run through a great comparison on the love of man and wife as equal to or similar to the love of Christ for His Church. The mystery that he seems to be referring to here is the mystery of Christ and His Church. I actually just wrote a paper on "The Universal Church or the Local Church" and this passage came up. I'd post the paper but some folks from other areas would not appreciate it...
Albert Barnes has a good portion on this in his commentary..
Verse 32. This is a great mystery. The Latin Vulgate translates this, sacramenturn hoc magnum est--" this is a great sacrament"--and this is the proof, I suppose, and the only proof adduced by the Papists, that marriage is a sacrament. But the original here conveys no such idea. The word mystery--musthrion--means something which is concealed, hidden, before unknown; something into which one must be initiated or instructed before he can understand it. It does not mean that it is incomprehensible when it is disclosed, but that hitherto it, has been kept secret. When disclosed it may be as intelligible as any other truth. See the word explained Cmt. on Eph 1:9. Here it means, simply, that there was much about the union of the Redeemer with his people resembling the marriage connexion, which was not obvious, except to those who were instructed; which was obscure to those who were not initiated; which they did not understand who had not been taught. It does not mean that no one could understand it, but that it pertained to the class of truths into which it was necessary for one to be initiated in order to comprehend them. The truth that was so great a mystery was, that the eternal Son of God should form such an union with men; that he should take them into a connexion with himself, implying all ardour of attachment, and a strength of affection, superior to even that which exists in the marriage relation. This was a great and profound truth, to understand which it was necessary to receive instruction. No one would have understood it without a revelation; no one understands it now except they who are taught of God.
But I speak concerning Christ and the Church. This, it seems to me, is an explicit disclaimer of any intention to be understood as affirming that the marriage contract was designed to be a type of the union of the Redeemer and his people. The apostle says expressly, that his remarks do not refer to marriage at all when he speaks of the mystery. They refer solely to the union of the Redeemer and his people. How strange and unwarranted, therefore, are all the comments of expositors on this passage designed to explain marriage as a mysterious type of the union of Christ and the church! If men would allow the apostle to speak for himself, and not force on him sentiments which he expressly disclaims, the world would be saved from such insipid allegories as Macknight and others have derived from this passage. The Bible is a book of sense; and the time will come, it is hoped, when, freed from all such allegorizing expositions, it will commend itself to the good sense of mankind. Marriage is an important, a holy, a noble, a pure institution, altogether worthy of God; but it does not thence follow that marriage was designed to be a type of the union between Christ and the church, and it is certain that the apostle Paul meant to teach no such thing.
)
