"This is a great mystery: but I speak concerning Christ and the church." (Ephesians 5:32)
The error of eros
Paul has just finished lining out the Christian concept of marriage. Almost by way of admission does he add the above. A "great mystery", he says, right after quoting Genesis (2:24). Jesus does the same in Mark's Gospel (10:7). "For this cause shall a man leave his father and mother, and cleave to his wife." Not that Paul is superseding what Jesus said. In much the same way Christ expounded from Genesis the point of a match made in Heaven, Paul comes after and expounds for the Ephesians what the whole point is. That we would learn through the give and take of a marriage covenant, the relationship between Jesus and ourselves, as His bride.
"Draw me, we will run after thee: the king hath brought me into his chambers: we will remember thy love more than wine: the upright love thee." (Song of Solomon 1:4)
O, my God. That is so supercharged as to render the most calloused of hearts splayed out and ready for romance. Or is it? A cursory reading would see it as a beautiful love poem infused with the sights and smells of Ancient Israel. In turn, a modern reader may be hard-pressed to then go one further and see it as symbolic of our relationship with Christ—especially when presented with the reality (and the why) of Christ's death and resurrection. While Solomon's Song is chock-full of allusion and metaphor and simile, pinning down a flat-out and overtly sexual meaning is almost a waste of time. Just because it uses the word "love" and "loves", doesn't mean it doesn't only mean the kind of love Christ shows us. Life is over so quickly and therefrom, the real difficulty arises. It isn't about coupling and copulating and cohabitating. It's about meeting and knowing Christ.
Agape over agape
"But He said unto them, All men cannot receive this saying, save they to whom it is given." (Matthew 19:11)
"For I would that all men were even as I myself. But every man hath his proper gift of God, one after this manner, and another after that." (1 Corinthians 7:7)
Evidently Paul had "receiv[ed] this saying". He had found such grace in the eyes of the Lord, knowing what God had done for him by way of atonement that the inverted void of seeking out a mate had been sated and silenced. And filled. It can be hard, extraordinarily hard, to so orient yourself around an eminently spiritual way of looking at life that you essentially forget you don't have a significant (human, physical) other. This is why Jesus says "all men cannot". Because if you want or need someone, if God made someone for you and you know this like you know yourself, then Jesus will be either/or until the right one comes along. So easy to read, a little harder to write. Impossible to live without help from on high. And when Paul says "This is a great mystery", I think he knows what He's talking about. To him, "To live is Christ, and to die is gain." (Philippians 1:21) Somewhere in the middle he had evidently given his heart to Jesus, the one who gave the same for humanity and then the deal was sealed. If you haven't for yourself, I strongly urge you to meet Jesus and to "comprehend with all saints what is the breadth, and length, and depth, and height; And to know the love of Christ, which passeth knowledge, that ye might be filled with all the fulness of God." (Ephesians 3:18b-19, emphasis mine). Any and every type of knowledge.
It's the only thing in life greater than finding your soulmate.
"And he saith unto me, Write, Blessed are they which are called unto the marriage supper of the Lamb. And he saith unto me, These are the true sayings of God." (Revelation 19:9)