Mary is in labor. Remember? Joseph finds a cave and gets her settled in it, leaves his sons to take care of her and runs off trying to find a Hebrew midwife.
For those of you wondering where the barn and manger are...those just aren't historically accurate, m'kay? Wood was scarce. They did not house their livestock in buildings made of wood. Caves on the other hand were really convenient and could be converted into 'barns'. So, Christ was born in a cave. Adjust. Orthodox icons have always depicted the Nativity in a cave and there's a kind of symmetry, with the infant Christ wrapped in white swaddling against the black mouth of the cave and then the knowledge that He will again be wrapped in cloth and laid in a cave for three days.
Oddly, the narrative switches to first person at this point. Some have said that it's proof that the Gospel is different texts merged together, but the oldest surviving fragment, from the fourth century runs from chapter 13 through 23 and contains the same shift. So if it is a merger of different texts it was a very early merger. It might just be a dramatic shift. Everything up to this point has been almost a prologue, how Mary was born, how she married Joseph, the Annunciation and their trial. Important, but not the 'main event'. For that, it might be more engaging if you hear the story being told as though the person speaking had been there.
I'm just going to copy the text. This is Joseph's point of view while trying to go find a midwife for Mary. He doesn't know it at the time, but this is also the moment of Christ's birth: "Then I, Joseph, was walking, but somehow I did not walk. I looked up into the vault of the heavens, and saw it standing still, and into the air and saw it astonished, and the birds of the heavens motionless. And I looked upon the earth and saw a platter resting, and workmen reclining, and their hands were in the dish. But the ones who were chewing did not chew, and the ones reaching did not reach, and the ones carrying food to their mouths did not carry it; but all their faces were looking upward.
"And I saw sheep being driven, yet the sheep stood still; and the shepherd raised his hand to strike them with his staff, and his hand remained up. And I looked upon the water-brook and I saw the kids put their mouths down upon the water and not drink. And suddenly all things moved forward in their course."
So time stopped.