The birth of Jesus Christ took place in this way: Mary, his mother, was pledged to be married to Joseph; but before they came to live together, she was found to be with child through the Holy Spirit. Joseph, her husband, was a righteous man and did not want to disgrace her publicly, so he decided to divorce her quietly. But as he was considering this, an angel of the Lord appeared to him in a dream and said: “Joseph, son of David, do not be afraid to take Mary, your wife, into your home. Though she is expecting a child through the Holy Spirit, you are to name the son she will bear. And you shall call him Jesus, for he will save his people from their sins.” All this took place to fulfill what the Lord had spoken through the prophet: “The virgin will conceive and give birth to a son, and they will call him Emmanuel, which means ‘God with us.’” When Joseph woke up, he did what the angel of the Lord had commanded him and took Mary into his home as his wife. But he did not consummate the marriage until she gave birth to a son. And he named him Jesus. (Matthew 1, 18–25)

This scene is based on the account from the Gospel of Matthew, we see the moment when Joseph, upon learning of Mary's pregnancy, doubts her fidelity and decides to dismiss her quietly. He appears lying in his bed, because while he was sleeping an angel appeared to him to confirm that Mary has conceived through the power and grace of the Holy Spirit, and that she will give birth to a son who will save his people. The angel asks him to name the child, that is, to accept him as his own and bring him into his lineage, the line of King David.