The little girl was standing with her grandmother near the train tracks at Coventry Road, as my husband and I approached. The wide-eyed child could not contain her excitement, and as we drew nearer, she exclaimed, “I saw a real train!”

For a child, the world is new, moment by moment. Leaves trembling on trees, clouds shaped like bears and bridges and bells: These are all causes for cheer. But adults see the train and the trees thousands of times and hardly heed them.

For me, one of Christ’s most riveting remarks was, “Unless you be converted and become as little children, you shall not enter into the kingdom of heaven.” This statement reminds me of the time Christ said how hard it would be for a rich man to enter heaven—as difficult as a camel passing through the eye of a needle.

Christ’s remark about little children comes home to me each Advent, as the weeks toward Christmas unfold. An all-powerful God could have engineered the Incarnation quite differently. He could have entered the world as a full-grown man, someone with incredible powers along the lines of a modern-day superhero like Superman or Batman.

Instead, he came as a baby with no extraordinary physical prowess at all. He was dependent on others to feed and clothe him, and protect him from Herod’s bloodthirsty soldiers. And these facts reveal a marvelous mystery and a momentous message: Even adults who pride themselves on worldly wisdom and wealth still rely on God for their next breath.

But how shall we become like children again? A little child lives in a world where anything is possible. A child believes stuffed animals come alive at night, and searches for elves in the yard. At some point, though, we cross the line into adulthood. We put away our tales and toys, and admit that no amount of kissing will transform a toad into a prince.

But for those who have faith, a secret kingdom in the heart remains open to miracles and marvels. As writer G.K. Chesterton put it, “Faith means believing the unbelievable. Hope means hoping when everything seems hopeless.”

Smug skeptics mock the miracles, though, and shun the splendor. “You think God came into the world as a baby?” They ask. “Impossible!” They shout. And “Bah humbug!”

Still, I imagine a skeptic peering into the manger at Christmas and having the fleeting thought:

“What if God did send his Son as a baby? Wouldn’t it be just like God to turn our expectations upside down?”

And that’s what it means to change our hearts. We have to drop cynicism and embrace trust. Stop grasping for wealth and be grateful for what we already have. Stop trying to engineer the future—and instead recognize what a child already knows.

A child senses that a parent is powerful. A child trusts that a parent’s love is endless, and believes the parent will provide for now and tomorrow. Once we truly see God this way, as our loving Father, we begin the transformation necessary to find the kingdom. Believing the unbelievable and hoping when all seems hopeless: This conversion of heart is the key to following Christ into the heavenly kingdom.

And it all makes perfect sense, you see, because Christ came into the world as a helpless child to show us the way. To teach us that with God, everything truly is possible. And if we hold that thought in our hearts, we can regain our own childhood wonder. We can stop trembling in fear and start trusting in faith.

We can recapture the awe of that little girl seeing the train, as we peer into the manger on Christmas Day, and pretend the figure of the baby has come to life, for just a second. And a simple heartfelt prayer can turn our serious adult world upside down just long enough to plant our feet firmly on the path to heaven: “My Lord and my God!”