God’s rules have been clear from the beginning: one husband, one wife.
“Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh.” (Gen 2:24).
Jesus commented on this:
“So they are no longer two but one flesh. What therefore God has joined together, let not man separate…. And I say to you: whoever divorces his wife, except for sexual immorality, and marries another, commits adultery.” (Matthew 19:6,9)
“Anyone who divorces his wife and marries another woman commits adultery against her. And if she divorces her husband and marries another man, she commits adultery.” (Mark 10:11-12)
“Each man should have his own wife and each woman her own husband.” (1 Cor 7:2)
“To the married I give this charge (not I, but the Lord): the wife should not separate from her husband (but if she does, she should remain unmarried or else be reconciled to her husband), and the husband should not divorce his wife.” (1 Cor 7:10-11)
“Each one should remain in the condition in which he was called.” (1 Cor 7:20)
So the principle is very clear: you should not get remarried even if circumstances force you to get a divorce.
In a perfect world, divorce wouldn’t happen, and every marriage would be a wonderful happy place…. but real world experience tells us otherwise — so much anger and fighting that can’t be resolved. And, perhaps, in an almost perfect world, people wouldn’t get lonely after getting divorced.
Well, the simple principle is not all the Bible says about divorce and remarriage. In practice, there are several caveats. For instance, where Jesus says “except for marital unfaithfulness” above. Another is Paul saying:
“But if the unbelieving partner separates, let it be so. In such cases the brother or sister is not enslaved. God has called you to peace.” (1 Cor 7:15)
Then there’s the fact that the Law of Moses allowed for divorce, even though God hates divorce (Mal 2:16). Jesus explains this:
“Because of your hardness of heart Moses allowed you to divorce your wives, but from the beginning it was not so.” (Matt 19:8)
Finally, there were some circumstances in which God mandated divorce — or appeared to. (Ezra 10:19; Jer 3:8).
It’s natural for people to seek simple rulebooks to follow, to know when it’s ‘ok’ to remarry, and Christians can get mighty hung up on this — especially on how far these various caveats apply. Don’t get caught like that: God gave us a clear principle, and the exceptions don’t establish a set of rules about when it’s ‘ok’; instead, they demonstrate that God is merciful when we demonstrate how human we are.