The book of Genesis speaks of the man leaving his father and mother and being united to his wife, and they will become one flesh (Gen. 2:24). When asked about divorce (Matt. 19:3), Jesus cited this passage and commented, “So they are no longer two, but one. Therefore what God has joined together, let no one separate” (Matt. 19:6).
The sad reality, however, is that sexual immorality does occur, and Jesus acknowledged that adultery comes between the marriage partners (the so-called “exception clause,” Matt. 19:9; cf. 5:32). Not as a command, but as a concession, Jesus permitted divorce, and remarriage, in those instances. (The “betrothal view” says Jesus only spoke of breaking an engagement in case of sexual immorality, but clearly the Pharisees’ question and Jesus’ answer, while possibly including engaged couples, related more broadly to marriage in general.)
To this Paul adds a second scenario in which divorce is permissible (the so-called “Pauline privilege”). If someone becomes a Christian and the unbelieving spouse refuses to continue in the marriage, “The brother or sister is not bound in such circumstances” (1 Cor. 7:15). Arguably, “not bound” means also “free to [re]marry” (1 Cor. 7:39).
On a pastoral level, we must take care to hold people to a high view of marriage, while at the same time not imposing on them a standard that is more rigid than Scripture itself (as a “no divorce under any circumstances” position would). If Jesus and Paul could uphold a high view of marriage while acknowledging exceptional cases in which divorce and remarriage were permissible, we should be able to do the same.
Marriage is not a sacrament, and while it contains covenantal features, it is a relationship between two human beings and not indissoluble under any circumstances. For this reason we must be mindful, not only of the potential pitfalls of too low a view of marriage, but also of the dangers of imposing on people a standard that is more rigid and absolute than Scripture itself.
For a fuller treatment of divorce and remarriage, see my essay in Marriage and Family in the Biblical World, 256–64 (including a critique of John Piper and the “betrothal view” on pp. 258–61) and Chapter 11 in God, Marriage & Family.