The word “manger” is mentioned three times in Luke’s account of the birth of Jesus. In Luke 2:12 it says it is a sign!

"And she brought forth her firstborn son, and wrapped him in swaddling clothes, and laid him in a manger; because there was no room for them in the inn. ... And this shall be a sign unto you; Ye shall find the babe wrapped in swaddling clothes, lying in a manger. ... And they came with haste, and found Mary, and Joseph, and the babe lying in a manger." - Luke 2:7, 12, 16

What could this sign be?

According to Thayer’s Lexicon, the word “crib” is another word for “manger”. It means feeding trough. "Crib" is found in Isaiah 1:3.

"Hear, O heavens, and give ear, O earth: for the LORD hath spoken, I have nourished and brought up children, and they have rebelled against me. The ox knoweth his owner, and the ass his master's crib: but Israel doth not know, my people doth not consider." - Isaiah 1:2-3

Rebellion brings spiritual blindness. It appears the Lord is revealing that because of rebellion, Israel would not recognize their Savior.

When Jesus ministered among His people, Israel did not recognize that Jesus is God.

The Bible says the ox and the donkey at the manger had more understanding than the Lord’s own people.

“An ox knows its owner, and a donkey its master’s manger, but Israel does not know, My people do not understand.” (NLT)

"He was in the world, and the world was made by him, and the world knew him not. He came unto his own, and his own received him not." - John 1:10-11

"But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name: which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God." - John 1:12-13 KJV (John 3:3, 5; Acts 2:38)

"Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God: therefore the world knoweth us not, because it knew him not." - 1 John 3:1 KJV