Question: When is remarriage permitted in Scripture?
Short Answer#1: Remarriage is sanctioned by scripture when a marriage is terminated either by Death (Romans 7:1-6), or Divorce if, and only if, there were biblical grounds (Matthew 19:9).
Then there is this question: Can two Christians marry even if one or both was previously divorced without biblical grounds?
The short answer to this question is that what we did before we were saved is washed away by the blood of Christ! Believers are new creatures in Christ, old things have passed away. (2 Corinthians 5:17) Hallelujah!
The longer answer includes the following:
Sometimes the consequences of sins committed before receiving Christ cannot be avoided. Crimes committed are still subject to penalties. Children born out of wedlock, or in former marriages, are still our children. Once a person comes to Christ and past sins are forgiven, believers should be all the more diligent to accept responsibility for the consequences of past sins--even though the penalty before God has been paid in full by Christ!
Individuals must be honest with the Lord and with themselves, however, since some may claim to have been born again after divorcing, when in fact that were born again before the divorce. If the "I did it before I was saved," argument is being claimed, it must be true, not a loophole.
This brings up another similar question. Can a person who was a Christian when he or she obtained an unbiblical divorce, not knowing it was sinful, ever be free to remarry? Here again, care must be given.
Under the Old Testament Law (Leviticus 4), God is clear that ignorance is not an excuse for sin. This is why the Law required sin offerings specifically for unintentional sin.
If the previous spouse is a believer and the two are willing, I would encourage them to explore the possibility of reconciling and remarrying.
If the previous spouse is not a Christian, the believer should do all he/she can to seek forgiveness and make things right, though remarrying a non-believer would not be the right thing to do.
If the previous spouse is a Christian or not, and if that previous spouse has remarried, I would say that in most cases, the believer may remarry someone else.
The question of remarriage to someone other than the previous spouse is even more complicated when there are children involved. In such cases, I would say previously divorced people need to put their children's best interests ahead of their own desires for a second marriage.
There are no doubt more scenarios than have been considered here. I trust that it is obvious that divorce and remarriage is complex and messy, and there are seldom one-size fits all answers. May we as believers be reminded of why God hates divorce! These knotty matters are best untied with direction from a biblically minded pastoral counselor—who has a high view of the sanctity of “the Lord’s holy institution which He loves,” (Malachi 2:11) namely: the sacred covenant of marriage.
Important Footnote: What should people do who have divorced, and even remarried unbiblically? We cannot “un-ring the bell!” Because we cannot undo past sins, ask the Lord for forgiveness and do the right thing, going forward (which likely means asking for forgiveness of those who were hurt by past sin). Praise God that in Christ, all our sins have been forgiven! (Colossians 2:13-14)