I think birth of a baby to be a serious challenge for the young family.
First, the pregnancy... It's easy to love your wife when she feels good. And it's a test for you love and patience when she cries for no reason and her mood changes from happy to bad dozens times a day. In these months I realized my husband to be the most loving and patient man I ever knew.
And then, the baby... It's easy to love your cute newborn son when he's happy and cheerful. But it's a test for your love and patience when he cries for hours on your hands. Less than two months passed since our son was born and I know that my husband is also a loving and patient father. I also discovered lots of patience in myself, that's strange. I've never been like that before.
And when you have a baby every day you see something new. The little one develops with great speed. He's interested in everything. Every new sound, object or face catches his attention. And some of the objects he even tries to grab and to eat :)
Being a mother is wonderful and birth of a baby is that experience than really makes you work for improving yourself.