“'Rise, take the child and his mother, and flee to Egypt, and remain there until I tell you, for Herod is about to search for the child, to destroy him.' And he rose and took the child and his mother by night and departed to Egypt."
That's what it says in the Gospel of Matthew... In Carpaccio's picture it is already morning. Joseph, Mary, the baby Jesus and the donkey must have been on the road for hours. In the hilly landscape through which they walk there are many rivers on which boats float. The landscape looks like the area around Venice.
Carpaccio is relying on the recognition effect here: merchants who visited Venice would have recognized the landscape immediately. Carpaccio shows people something from their everyday lives. He brings the story from the Bible into their present day. This is intended to bring the story to life for the people of Carpaccio's time. The precious fabric of Mary's cloak could also be a reference to Venice; many families from Venice became rich through trading in fine fabrics.
Unfortunately, we no longer know anything about the person who commissioned the painting. We assume that the painting hung in a private household and was used for prayers at home – perhaps by a wealthy merchant family?