Concerning marriage, it must be said that it is the one-ness or unity of the relationship that grounds its permanency, connoting an indivisible entity in the cohesion of the former two; and, this perpetuity of the unit itself is grounded in the nature of the relationship being made in the image of God, as it reflects the triune interrelationships within the Godhead, known by the archaic theological term, perichoresis. My reasons for these convictions are reflected in what follows.
The marriage is the primary covenantal, social unit; the married couple too is a triune God image-bearing reality. Jesus made it clear that spiritual/covenantal relations take precedence over biological ones (Matt 12:48—50). Marriage is just such a relationship.
This is further buttressed by the language and thrust of Gen 2:24, which Jesus (Matt 19:5 // Mk 10:7) and Paul (Eph 5:31) both cite in their teaching on the meaning of marriage. The language of “leave” and “cleave” in these texts could not be stronger. “Leave” is an active indicative verb, meaning to leave behind, depart from, abandon, forsake, and so on. The object of this verb, as you know, is “his father and his mother.” Contrariwise, the term “cleave” or “hold fast” means to glue together, to laminate, etc., thus creating a whole new unit that is stronger than its parts individually.
Furthermore, following Genesis, Jesus prefaces these remarks with “for this reason” or “therefore.” So, the purpose or reason for man’s creation as complimentary man and woman is the marriage covenant. And since humanity, in general, was created to reflect God’s glorious image throughout creation; and, man’s creation in two sexes is to be glued together in the marriage covenant, it is not hard to see how the marriage covenant is to be a reflection of God’s tri-unity.
The purpose of creating two sexual identities is that they leave and cleave—marriage. The very next verse (Matt 19:6) begins with the conjunction ‘so,’ “so they are no longer two but one flesh.” This conjunction is signaling the purpose/result of the marriage union—two distinct persons becoming one flesh, one being! Distinct persons sharing a single being, sound familiar? That’s right, the Trinity! This “oneness” and the strength of this language and reasoning has only one other analogy in our experience.
The only other relationship that we can have in life that speaks with this sort of solidarity and uncompromising commitment is our union with Jesus himself. In Lk 14:26, Jesus says that unless we are willing to completely abandon our filial relationships for his sake and the kingdom’s, we cannot be his disciples. Our love for him will so pale all other relationships as to make them seem as hatred; so also with a man and his wife. This is precisely why Paul could use Christ’s relationship to the Church as a corresponding analogy for covenantal marriage, and vice versa (Eph 5:22ff).