Gibbs, Jeffrey A. “Matthew 5:31-32: On Divorce." St. Louis: Concordia Publishing House, 2006, pp. 290-296.
In Matthew 5:31-32, Jesus speaks of divorce. Gibbs quotes a first century example of a write of divorce (Gibbs 2006, 290). The assumption in the document is that the woman will remarry. The term Jesus uses to describe the outcome, porneia, probably refers to a sexual relation with someone who is married to someone else. Of interest to Gibbs is the implication that the husband who issues the divorce provokes his former wife to endure adultery (Gibbs 2006, 291). He is the one guilty of the adultery.
The issue arises again at greater length in Matthew 19:3-12. In this briefer passage, Gibbs considers Jesus to be speaking specifically of the husband's responsibility. The concept is predicated on Deuteronomy 24:1-4, where Gibbs observes that it is permited for a man to divorce his wife but not to take her as his wife again (Gibbs 2006, 292-293).
At the time of Jesus' teaching there was a debate between the schools of Hillel and Shammai. The followers of Shammai saw the reason for divorce as a woman's adultery, while Hillel took it to be "indecency," which could include any sort of indecorum. Gibbs concludes that the Hillel interpretation was the most accepted at the time of Jesus' statements (Gibbs 2006, 293).
Gibbs sees Jesus as affirming that marriage and divorce involve more than "a measure of protection and future security" (Gibbs 2006, 294). The divorce breaks the union created by God. For this reason, it could be seen as an act of adultery. Unlike adultery, Gibbs observes divorce causes more harm because reconciliation is no longer an option (Gibbs 2006, 295). Gibbs does not take the passage to mean that an innocent party to a divorce should be unable to marry. However, he does see the passage as a statement that divorce is seriously harmful by nature. For this reason, Jesus compares it to the grave sin of adultery.