As presented in the Synoptics, Jesus' teaching on divorce provides an interesting case (Matt 19:1-12; Mark 10:1-12; Luke 16:18; see 1 Cor 7:10-16). Luke only includes one saying, whereas Matthew and Mark provide a full scene on the subject. What do we learn?
First, we're talking not about Scripture but about the appropriation of traditions going back to Jesus. Note that Mark, presumably addressing a largely Gentile audience where women could initiate divorce, envisions contexts when a woman might divorce a man. Matthew, presumably addressing Jewish followers of Jesus, does not. We may never know what Jesus himself said about divorce -- maybe he spoke to the question on multiple occasions -- but that's not the point. The point is that both Mark and Matthew appropriated traditions concerning Jesus' teachings to address their own cultural contexts.
And Paul? Paul apparently knows the same tradition. There are three steps to his argument.
- In 1 Cor 7:10-12 he relies upon a word from the Lord to command women not to divorce their husbands.
- However, admitting people will divorce anyway, he continues to rely on Jesus tradition: If a woman leaves her husband, she ought not marry someone else.
- Finally, in 7:13-16 Paul addresses an entirely new context. Jesus could not have been speaking to "believers" married to "unbelievers," since there were no "believers" in Jesus' own day. Paul must address the situation, but here he speaks in his own authority: "I and not the Lord."