Marriage is a vocation that is not for all, because it demands radical union of soul and body with another, but this also makes it a powerful sign of the union that God wants for all of humanity in the end.
Based on Matthew 19:3-12:
Some Pharisees came to Jesus, and to test him they asked, ‘Is it lawful for a man to divorce his wife for any cause?’ He answered, ‘Have you not read that the one 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 they are no longer two, but one flesh. Therefore what God has joined together, let no one separate.’ They said to him, ‘Why then did Moses command us to give a certificate of dismissal and to divorce her?’ He said to them, ‘It was because you were so hard-hearted that Moses allowed you to divorce your wives, but at the beginning it was not so. And I say to you, whoever divorces his wife, except for unchastity, and marries another commits adultery.’
His disciples said to him, ‘If such is the case of a man with his wife, it is better not to marry.’ But he said to them, ‘Not everyone can accept this teaching, but only those to whom it is given. For there are eunuchs who have been so from birth, and there are eunuchs who have been made eunuchs by others, and there are eunuchs who have made themselves eunuchs for the sake of the kingdom of heaven. Let anyone accept this who can.’
(New Revised Standard Version Bible: Anglicized Edition, copyright © 1989, 1995 National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved worldwide. http://nrsvbibles.org)