Perhaps an audience of Jewish listeners would have resonated with Jesus’s statements on murder (5:21-26) and adultery (5:27-30). At least in principle everyone can agree that anger and lust are the internal motivations for the external sins of murder and adultery. Even if one is not a follower of Jesus, controlling anger and lust is a positive and healthy goal. Greek philosophy encouraged people to balance their passions and to be in control of their inner thoughts.
But when Jesus taught on divorce and oath-making, he was challenging accepted practices of the Jewish world of the first century. It is likely few people who heard Jesus teach were adulterers and maybe no one was a murderer. But divorce was a far more common issue and everyone has made a promise or two they regretted and would like to have a legal way out of their oath. For some in the original audience, Jesus has moved from preaching to meddling.
After writing over one hundred pages on Jesus’s view of divorce, John Meier comments his prohibition of divorce would have disturbed his otherwise sympathetic listeners (Marginal Jew, 3:182). The same is true for his prohibition of oath-making in Matthew 5:33-37. As Meier points out, no Jewish teaching in the first century completely prohibited making oaths and vows. Even the closest parallel to Jesus, the Essenes, swore vows to obey the rules of the Community. The Pharisees would have reacted strongly to Jesus’s teaching on both divorce and oath-making (Meier, 3:205). Unfortunately we do not have their side of the argument, nor does Jesus explain his rationale for making these sweeping prohibitions.
It would appear the earliest Christians either did not know Jesus’s prohibition on oaths or they interpreted it differently. Paul made oaths in his letters. For example, 1 Corinthians 1:23, God calls on God as a witness, more or less swearing his claims are true by invoking God! Similarly, in Philippians 1:8 he says “with God as my witness.” The book of Acts appears to describe him taking a Nazarite vow (Acts 18:18) and later participating in the conclusion of vows (Acts 21:26). The writer of Hebrews refers to swearing an oath by something greater (6:16). Although the command against oath making was taken literally in the early days of the church, by the Middle Ages “the entire tradition of the major churches has almost uniformly disregarded Matt 5:33-37 and accepted oaths, even if it often did so with a bad conscience” (Matthew 1-7, 267–268).
So Jesus says “do not swear an oath at all” and the rest of church history figures out ways around the command. In his recent commentary on the Sermon on the Mount, Jonathan Pennington says “Jesus is not overturning or abolishing the original commandment. He is not opposed to oath or vow making” (293). Charles Quarles argues Jesus prohibited “misleading oaths” intended to allow a person to break their promise if it was to their advantage (Sermon, 144). For Pennington, oaths and vows can be made only if the disciple of Jesus intends to fulfill them.
These interpretations allow Christians to serve in the military (which demands oaths) or give testimony in court, or even have a mortgage, which is more or less an oath to pay back a loan. Modern society demands oath-making, so we have to find some way to deal with Jesus’s actual words. Modern society demands the possibility of divorce, so we need to find a way around Jesus’s actual words.
But did Jesus intend for his disciples to find ways around his words when modern culture finds them too inconvenient? I would suggest the ideal disciples of Jesus honor marriage in such a way that divorce is not an issue; the idea disciple honors truth to the point there is no need for making an oath. For the ideal disciple of Jesus, all their words are “with God as my witness.”