Catholics and Protestants, alike, usually want to know what the biblical foundation is for the Catholic Church's stance on marriage, and particularly, the practice of granting declarations of nullity of marriage. And so, we would like to walk through a number of passages of scripture and explain the Catholic position.
Power of the Church
If your brother sins [against you], go and tell him his fault between you and him alone. If he listens to you, you have won over your brother. If he does not listen, take one or two others along with you, so that 'every fact may be established on the testimony of two or three witnesses.' If he refuses to listen to them, tell the church. If he refused to listen even to the church, then treat him as you would a Gentile or a tax collector. Amen, I say to you, whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven.'
The above passage from Matthew shows that Christ gave the Church authority to settle disputes. St. Paul further elaborates on this and tells us that the Church should set up a court system to judge cases.
How can any one of you with a case against another dare to bring it to the unjust for judgment instead of to the holy ones? Do you not know that the holy ones will judge the world? If the world is to be judged by you, are you unqualified for the lowest law courts? Do you not know that we will judge angels? Then why not everyday matters? If, therefore, you have courts for everyday matters, do you seat as judges people of no standing in the church? I say this to shame you. Can it be that there is not one among you wise enough to be able to settle a case between brothers? But rather brother goes to court against brother, and that before unbelievers?
I Cor 6:1-6
Divorce in the Bible
The Old Testament never commands divorce. Rather, it treats divorce as an unfortunate reality which has arisen due to the hardness of people's hearts. In fact, God says:
You must then safeguard life that is your own, and not break faith with the wife of your youth. For I hate divorce, says the Lord, the God of Israel, and covering one's garment with injustice, says the Lord of hosts.
Jesus reveals to us that not only is divorce unfortunate, but in fact, divorce has no power to break the bond between man and woman. Jesus reveals that if a couple divorce they are still tied to one another through the unbreakable bond of marriage:
He set out from there and went into the district of Judea [and] across the Jordan. Again crowds gathered around him and, as was his custom, he again taught them. The Pharisees approached and asked, 'Is it lawful for a husband to divorce his wife?' They were testing him. He said to them in reply, 'What did Moses command you?' They replied, 'Moses permitted him to write a bill of divorce and dismiss her.' But Jesus told them, 'Because of the hardness or your hearts he wrote you this commandment. But from the beginning of creation, 'God made them male and female. 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 they are no longer two but one flesh. Therefore what God has joined together, no human being must separate.' In the house the disciples again questioned him about this. He said to them, 'Whoever divorces his wife and marries another commits adultery against her; and if she divorces her husband and marries another, she commits adultery.'
Everyone who divorces his wife and marries another commits adultery, and the one who marries a woman divorced from her husband commits adultery.
It was also said, 'Whoever divorces his wife must give her a bill of divorce.' But I say to you, whoever divorces his wife (unless the marriage is unlawful) causes her to commit adultery, and whoever marries a divorced woman commits adultery.
When Jesus finished these words, he left Galilee and went to the district of Judea across the Jordan. Great crowds followed him, and he cured them there. Some Pharisees approached him, and tested him, saying, 'Is it lawful for a man to divorce his wife for any cause whatever?' He said in reply, 'Have you not read that from the beginning the Creator '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 they are no longer two, but one flesh. Therefore, what God has joined together, no human being must separate.' They said to him, 'Then why did Moses command that the man give the woman a bill of divorce and dismiss [her]?' He said to them, 'Because of the hardness of your hearts Moses allowed you to divorce your wives, but from the beginning it was not so. I say to you, whoever divorces his wife (unless the marriage is unlawful) and marries another commits adultery.' [His] disciples said to him, 'If that is the case of a man with his wife, it is better not to marry.' He answered, 'Not all can accept [this] word, but only those to whom that is granted. Some are incapable of marriage because they were born so; some, because they were made so by others; some, because they have renounced marriage for the sake of the kingdom of heaven. Whoever can accept this ought to accept it.'
St. Paul teaches the same basic reality: divorce does not separate the couple, they are still bound to one another:
To the married, however, I give this instruction (not I, but the Lord): A wife should not separate from her husband—and if she does separate she must either remain single or become reconciled to her husband—and a husband should not divorce his wife.
I Cor 7:10-11
This does not mean that divorce is always to be avoided. Sometimes, divorce is necessary to preserve one's physical, emotional, or spiritual wellbeing. But if divorce occurs, it is governed by the biblical principle so clearly taught above, namely, that divorce does not destroy the bond of marriage.
Nevertheless, this principle only applies to true marriages. Reason tells us that if two people were only pretending to marry, then this biblical principle does not apply. Moreover, if the people were legally incapable of marriage, then the biblical principle does not apply. There are many possible reasons why a marriage could be "invalid," as we say.
The Church, having been given Christ's own power to judge, is the only body capable of determining authoritatively whether a given marriage was a true marriage or not.