Unfortunately, the world is moving further and further away from moral purity and more towards doing what is right in its own eyes. One of the symptoms of this moral decay is the increase in denial of the necessity of marriage.
First of all, we need marriage because God says we should be married. Marriage is not only for the benefit of the couple, but it is also for the children. When a husband and wife are bound by a public promise to stay faithful to each other, to remain dedicated to one another even through sickness and poverty, the marriage bond is a much stronger one, and this is vitally important because marriage is the foundation of society. It is the bedrock of moral development of children and the place where faithfulness and integrity are lived out in the lives of its participants.
If a man and woman live together without the benefit of marriage, they are saying that God is not correct and that marriage is not necessary. If they have children out of wedlock they are risking the children's moral and emotional health since the children will learn that convenience and self-serving ideals are more important than integrity. They will learn that personal preference is more valuable than the welfare of another. They will learn that selfishness is the model by which to live since the sacrifice of commitment to one person has not been made.
In addition, children need security and instruction. Marriage helps to secure the family bond thereby providing a more secure environment in which the children may grow so that they might properly learn morality and integrity as they enter into society as adults. After all, those parents who do not value marriage tend not to value commitment and children should not be raised where the parents are not committed to each other.
Furthermore, marriage with its promise of fidelity, helps to ensure health through the prevention of venereal diseases. Marriage helps to ensure the very sanctity of the spouse-to-spouse relationship since marriage is a public statement of exclusive dedication. This helps to establish a foundation in the relationship where a marriageless, living-together relationship can have no true trust since people are together out of convenience. If it becomes inconvenient, then they can easily break up -- children or no children.
Marriage is not just a piece of paper. It is a promise to live together faithfully, till death, through thick and thin, sickness and health, and it is a benefit to the children who are raised in it. Marriage is a blessing from God.