the bridegroom reference is also to the analogy that the "Church" is the "bride" of Christ, therefore making Christ the bridegroom.

The parallel between the coming of Christ and the return of the sun at the winter solstice is of long standing.(Obviously so, as here it appears in lyrics that are nearly 300 years old) It is one of the reasons that celebrating the birth of Christ near the Solstice is logical, even tho there were other more political considerations for placing the celebration then as well.