It is the child who reveals God to us, as in some ways every newborn reveals God to us, being made in their Creator's image. The mystery of salvation is the mystery of a child. A child is real, and not yet real, it is in history and not yet historical. It's nature is visible and invisible, it is here and not yet here. And just this is the character of salvation.
Salvation has the nature of a child.
In this sense, when Christ is born into our hearts, we have a new beginning, a second birth if you will. But salvation must be tended, nurtured, allowed to develop, and Christ takes form in each individual differently over time. Too many people never let the Christ within them grow beyond the manger. He is cute, sentimental, and occasionally crying with demand, but easy to control and making little impact on the person whose spiritual development has been arrested. But Jesus the Man is not to be seen.