Here are some quotes from St. Josemaria from Christ is Passing By on family and marriage which I want to share with you. It answers my questions on the purpose of marriage and the reason why it can be your/my path to sanctity.
Of course, there are couples to whom our Lord does not grant any children. If this happens, it is a sign that he is asking them to go on loving each other with the same affection and to put their efforts, if they can, into serving and working for the good of other souls. But the normal thing for a couple is to have children, who must always be their first concern.
Being a father or a mother is not simply a matter of bringing children into the world. The capacity for generation, which is a share in the creative power of God, is meant to have a continuation. Parents are called to cooperate with the Holy Spirit in the development of their children into men and women who will be authentic Christians.
The parents are the first persons responsible for the education of their children, in human as well as in spiritual matters. They should be conscious of the extent of their responsibility. To fulfil it, they need prudence, understanding, a capacity to love and a concern for giving good example. Imposing things by force, in an authoritarian manner, is not the right way to teach. The ideal attitude of parents lies more in becoming their children's friends — friends who will be willing to share their anxieties, who will listen to their problems, who will help them in an effective and agreeable way
Parents should find time to spend with their children, to talk with them. They are the most important thing — more important than business or work or rest. In their conversations, parents should make an effort to listen, to pay attention, to understand, to recognize the fact that their children are sometimes partly right — or even completely right — in some of their rebellious attitudes. At the same time, they should help their children to direct their efforts and to carry out their projects properly, teaching them to consider things and to reason them out. It is not a matter of imposing a line of conduct, but rather of showing the human and supernatural motives for it. In a word, parents have to respect their children's freedom, because there is no real education without personal responsibility, and there is no responsibility without freedom.