In the following quote from The Mystery of Marriage Mike Mason draws out the beauty of how marriage is the ultimate example of "iron sharpening iron."
What is most unique about the tenacious fidelity of marriage is that it allows for such a really brutal amount of "sharpening" to take place, yet in the gentlest way imaginable. Who ever heard of being sharpened against a warm, familiar body of loved flesh? Only the Lord could have devised such an awesomely tender and heartwarming means for men and women to be made into swords. Yet for all its gentleness, marriage is still a fire and a sword itself, a fire which brands, and a sword which inflicts a wound far deeper than any arrow of Cupid. For it is a wound in a person's pride, in a place which cannot be healed, and from the moment a man and woman first stand transfixed in one another's light they will begin to feel this wound of marriage opening up in them. The Lord God made woman out of part of man's side and closed up the place with flesh, but in marriage He reopens this empty, aching place in man and begins the process of putting the woman back again, if not literally IN the side, then certainly AT it: permanently there, intrusively there, a sudden lifelong resident of a space which until that point the man will have considered to be his own private territory, even his own body. But it marriage he will cleave to the woman, and the woman to him, the way his own flesh cleaves to his own bones.
Just so, says the Lord, do I Myself desire to invade your deepest privacy, binding you to Me all your life long and even into eternity with cords of blood.