When something great happens, we say, "Wow!" We certainly didn't expect it. We didn't necessarily deserve it. And before too long, we'll probably forget it. That's the only reason the church is here: As a temporary reminder of the world- and life-changing glory, grace, and mercy that even Christians are prone to forget. My Christmas sermon is here.
As for the wow of wows, the most important moment of revelation, the evangelists are all over the map, from the Resurrection to Bethlehem to the beginning of all things. When did you realize that the universe, despite all appearances to the contrary, was safe? When was your first Christmas? My sermon for the first Sunday after Christmas is here.