The traditional interpretation of Jesus' story is mankind is sinful and needed a savior. Some denominations teach that we are born with original sin, inherited from Adam, and there is no hope of being sinless. The sinless part is important because God can't tolerate sin and must punish the sinful. This is where Jesus comes in. He is a human sacrifice for the sin of the world. So the manger picture is a reminder that this child was born to be killed as a sacrifice to God for the shortcomings of mankind.
What if we missed it? What if that isn't what Jesus' intended as his message?