Concerning Matthew 19:9, I have a question.  If God’s law governs God’s people, then are unions between non-believers even considered marriage anyway?  If they aren’t, then would Matthew 19:9 apply to them?

It’s noteworthy that Jesus said, “WHOEVER divorces his wife, except for fornication, and marries another, commits adultery” (Matt. 19:9 – emphasis mine).  The same words in the Greek for “whoever” in Matthew 19:9 are used in other passages like “whoever murders will be liable to judgment” (Matt. 5:21) or “whoever denies me before men, I also will deny” (Matt. 10:33).  The term “whoever” is universal in scope, providing no exceptions.  The NIV uses “anyone,” and for good reason.  “Whoever” or “anyone” in this verse and those similar to it refer to anyone who would find themselves committing the action of the verb which is being discussed.  He did not specify that the directive found in Matthew 19:9 applies only to Christians and not to non-Christians.

And with good reason, because sin is defined as “lawlessness” (1 John 3:4).  It is impossible to sin if God has not made a law which one’s actions violate.  Paul said, “Where there is no law there is no transgression” (Rom. 4:15), and, “For apart from the law, sin lies dead” (Rom. 7:8).

If one operates under the assumption that God’s laws of divorce and remarriage, and marriage in general, apply only to those who believe in God and follow Him (Christians), then consistency would demand that all of the rest of God’s laws about anything and everything also apply only to Christians.  That being the case, anyone who is not a Christian would have no sin to begin with, since they would not have violated any of God’s laws because, being outside of Christ, God’s laws supposedly would not apply to them anyway.

This means they would have no reason to repent (Acts 17:30), for they would have nothing of which to repent.  They would have no need to be baptized for the forgiveness of sins (Acts 2:38), because they would have had no sins needing forgiveness.  There would not even be a need for Christ to die on the cross in the first place, when one takes this line of reasoning to its consistent and ultimate conclusion.

Therefore, God’s laws concerning marriage in general and divorce and remarriage in particular are universal in nature and apply to the non-Christian just as they apply to the Christian.