If you try to point out something to a dog, the dog will often look at your finger instead of the object you’re trying to point to. This is frustrating, but it illustrates a natural mistake we all make from time to time. It’s the mistake many people make when reading the Christmas story in Luke’s gospel.
We tend to think about the manger in this way - the Christmas crib. The most famous animal feeding trough in all history. You see it on Christmas cards. Churches make elaborate cribs and sometimes encourage people to say their prayers in front of them. We know about the animals even though Luke never mentions any nor is there any indication that the shepherds or Mary and Joseph brought any with them.
To concentrate on the manger and to forget why it was mentioned in the first place is like the dog looking at the finger rather than the object. Why has Luke mentioned it 3 times in the story?
The answer is: that it was the feeding trough, appropriately enough, which was the sign to the shepherds. It told them which baby they were looking for. It showed them that the angel knew what he was talking about. The reason Luke has mentioned it is because it’s important in giving the shepherds their news and their instructions.
Why is this significant? Because it was the shepherds who were told who this child was. That he was the saviour, the Messiah, the Lord. The manger isn’t what’s important. It’s a signpost, a pointing finger, to the identity and task of the baby boy who was lying in it. It may also have confirmed for Mary and Joseph who Jesus was to be because up until this point it had been their secret.
(NT Wright. Luke: For Everyone. Westminster John Knox Press: Kentucky. 2004. Page 21-22.)