Jesus and His disciples were preparing for the Passover meal.
Read: Mark 14:13, 15–16
And he sent two of his disciples and said to them, “Go into the city, and a man carrying a jar of water will meet you. Follow Him. And he will show you a large upper room furnished and ready; there prepare for us.” And the disciples set out and went to the city and found it just as he had told them, and they prepared the Passover.
The Passover meal was a time for Israel to remember how God saved them many years earlier. When death came to Egypt (where they were slaves), it passed over the homes of those who believed God and put the blood of a lamb on the doorposts. The lamb was a picture of what Jesus would do when He died in your place for your sin.