John Paul II speaks about the nature of paternity in a husband and father and maternity in a wife and mother, and of the special challenge that paternity brings with it:
 

Physically, a woman becomes a mother thanks to a man, while paternity in its psychological and spiritual aspects is the effect on a man’s interior life of a woman’s maternity.

 
I had to re-read that sentence about four times before I understood what he was saying, but now that I understand, it makes perfect sense. So what is the challenge of being a father?
 

The physical implications of paternity have a smaller place in the life of a man, and especially the life of his organism, than those of maternity in the life and the organism of a woman. For this reason paternal feelings must be specially cultivated and trained, so that they may become as important in the inner life of the man as is maternity in that of the woman, for whom the biological facts alone suffice to make it important.

 
Doesn’t that make impeccable sense? It does to me, and it explains why oftentimes I hear of fathers who don’t seem to “own up” to their paternity, who are somehow disconnected from it and instead of trying to specially cultivate and train themselves to appreciate it, alienate themselves from their own children.
 
So what are the blessings that await the couple who do foster their blessed maternity and paternity?

Both find in parenthood confirmation not merely of their physical but of their spiritual maturity, and a promise of the promulgation of their own existence. When their lives in the body cease, their child will continue to live–the child who is ‘flesh of their flesh’, and above all a human person whose inner self they have both helped to form, in whom they have fashioned that which above all determines personhood. For the person is much more an ‘interior’ than a ‘body’.

 
So we as men have the special challenge and honor of growing in deep appreciation of being a father, of being given the gift to father children and form them with our wives and God to become saints. This is for keeps! These children, like us, live forever! And how we rear them affects the salvation and fate of the entire world.