As I understand Matthew 19:9 and Matthew 5:32 concerning divorce, Jesus is answering the Pharisees (Jews) as they were tempting him on this question. His answer was the same as the law that they were under (except for fornication). Such as in the case that Joseph thought Mary was in.
Why do we in the church today use it as a scriptural reason for married persons and Christian to get a divorce? I have problems with this. Seeing that Jesus was speaking to the Jews under the Old Law and not to a Christian as He had not died. He told his apostles that the Holy Spirit would guide them into all truth after his ascension. The gospel books had not even been penned, and there is no account of this in the scriptures after the Church was established. In fact, bound until death is very plain for the Christian. So why do we use these scriptures to apply to a Christian today?
You are correct that the four gospels were penned after Jesus' death and resurrection. Now, I have a question for you: Why were they written if at the time of their writing anything they contained did not apply to Christians?
"The beginning of the gospel of Jesus Christ, the Son of God" (Mark 1:1).
When a testator dies, the will which he established before his death goes into effect with his death. "For where there is a testament, there must also of necessity be the death of the testator. For a testament is in force after men are dead, since it has no power at all while the testator lives" (Hebrews 9:16-17). After Jesus arose, he instructed the disciples, "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I have commanded you; and lo, I am with you always, even to the end of the age" (Matthew 28:19-20). Notice that they were commanded to teach what Jesus had already taught them. They expanded on what Jesus established, but they didn't add anything new. For example, prior to his death, Jesus taught: "A new commandment I give to you, that you love one another; as I have loved you, that you also love one another" (John 13:34). We understand that this applies to us as Christians.
What the Holy Spirit taught the disciples was not something new, but a reminder of what Jesus had already taught them. "But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all things that I said to you" (John 14:26).
While Matthew 19:9 was in response to a question from the Pharisees, Matthew 5:32 was not. Matthew 5:32 is a part of the Sermon on the Mount, the same sermon that you have no problems understanding regarding:
- persecution: "Blessed are you when they revile and persecute you, and say all kinds of evil against you falsely for My sake. Rejoice and be exceedingly glad, for great is your reward in heaven, for so they persecuted the prophets who were before you" (Matthew 5:11-12).
- influence: "You are the light of the world. A city that is set on a hill cannot be hidden" (Matthew 5:14).
- lust: "But I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart" (Matthew 5:28).
- prayer: "For if you forgive men their trespasses, your heavenly Father will also forgive you. But if you do not forgive men their trespasses, neither will your Father forgive your trespasses" (Matthew 6:14-15).
- righteousness: "Enter by the narrow gate; for wide is the gate and broad is the way that leads to destruction, and there are many who go in by it. Because narrow is the gate and difficult is the way which leads to life, and there are few who find it" (Matthew 7:13-14).
- obedience: "Not everyone who says to Me, 'Lord, Lord,' shall enter the kingdom of heaven, but he who does the will of My Father in heaven. Many will say to Me in that day, 'Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?' And then I will declare to them, 'I never knew you; depart from Me, you who practice lawlessness!'" (Matthew 7:21-23).
Yet, the most direct answer to your question is because Paul cites Jesus as proof for his teaching: "Now to the married I command, yet not I but the Lord: A wife is not to depart from her husband" (I Corinthians 7:10). Now, in case you've forgotten, Paul is referring to "And He answered and said to them, "Have you not read that He who made them at the beginning 'made them male and female,' and said, 'For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh'? So then, they are no longer two but one flesh. Therefore what God has joined together, let not man separate'" (Matthew 19:4-6). Now why can Paul prove his point by the Gospel account, but you wish to edit out Jesus' statement on the same topic which comes just three verses later? An answer that the disciples objected to, which Jesus said, "All cannot accept this saying, but only those to whom it has been given: For there are eunuchs who were born thus from their mother's womb, and there are eunuchs who were made eunuchs by men, and there are eunuchs who have made themselves eunuchs for the kingdom of heaven's sake. He who is able to accept it, let him accept it" (Matthew 19:11-12). To whom was this statement given? Since Jesus mentioned the kingdom of heaven (the church), is not his statement applicable to the church? Jesus knew the Jews would reject his statement but his church would accept it.
Yes, there are a few things mentioned in the Gospels that only applied to the Jews directly, things like taking offerings to the altar, sacrifices, and holy day observances. But it is incorrect to assume that all in the Gospels were meant only for the Jews. It is the opposite; the Gospels were written for Christians. They just happen to take place in a setting when the Old Law was still in effect.
Finally, you assume that divorce was unknown in the church, but the apostle Paul also taught regulations on divorce: "But even if she does depart, let her remain unmarried or be reconciled to her husband" (I Corinthians 7:11). He didn't have to go into the exception clause because Jesus, whom Paul cited, already covered that aspect of a divorce.