It sums up the gospel very nicely, especially if you include v. 13: "No one has greater love than this, to lay down one's life for one's friends." The nail marks remind us that God's love is entirely different from worldly love. Worldly love is self-serving; we are willing only to enter into a marriage as long as our partner is fulfilling our needs. When the seas get choppy, we jump ship. God's love is selfless; he fulfilled our deepest need, even though it cost him his life, and even though we could provide nothing in return.
Marriage is intended to be a picture of God's love for his precious bride, the Church. Christian marriages would not fall apart if each husband would realize that it is his duty to sacrifice of himself—his own comfort, his needs, and even his life, if necessary—for his wife. This sacrifice triggers a response of loving commitment from each wife, just as the Church responds to Christ's self-giving love. No spouse is perfect in fulfilling his or her role, of course, but then we may always look to Christ's forgiveness, and start each day anew in his grace.
