Afterward Jesus adds: “However, many that are first will be last, and the last first.” What does he mean?

He means that many people who are “first” in enjoying religious privileges, such as the rich young ruler, will not enter the Kingdom. They will be “last.” But many, including Jesus’ humble disciples, who are looked down upon by the self-righteous Pharisees as being “last”​—as being people of the earth, or ‛am ha·’aʹrets—​will become “first.” Their becoming “first” means they will receive the privilege of becoming corulers with Christ in the Kingdom.

“MANY that are first,” Jesus just said, “will be last and the last first.” Now he illustrates this by telling a story.