Jesus gave Peter and John a task but not an address. They needed to know where to go. Gill explains that they were not asking which town, since "it was a fixed and determined thing, that the passover should be eaten at Jerusalem, and nowhere else." They were asking which house in Jerusalem. It is a simple, practical question from two men ready to obey.

Jesus told them exactly what to do: "when ye are entered into the city, there shall a man meet you, bearing a pitcher of water; follow him into the house where he entereth in" (Luke 22:10). They were to ask the master of the house for the guestchamber, and he would show them "a large upper room furnished" (Luke 22:11-12). "And they went, and found as he had said unto them: and they made ready the passover" (Luke 22:13).

The Passover remembered Israel's rescue from Egypt. The Law said it could not be sacrificed "within any of thy gates," but only "at the place which the LORD thy God shall choose to place his name in" (Deuteronomy 16:5-6). By Jesus' day that place was Jerusalem, which is why Gill says the disciples were only asking which house.

The feast of unleavened bread followed the Passover. Barnes notes that "The feast continued eight days, including the day on which the paschal lamb was killed and eaten." Preparing meant getting the lamb, the unleavened bread, and the room ready for the meal.

This row is mostly about logistics, but the surrounding passage shows Jesus in full command of what is about to happen. He sends the disciples, He knows who they will meet, and everything happens "as he had said unto them" (Luke 22:13). Matthew Henry says the arrangement taught the disciples "to depend upon the conduct of Providence, and to follow that, step by step."

The meal they were preparing would be His last before He suffered. Jesus would tell them, "With desire I have desired to eat this passover with you before I suffer" (Luke 22:15).