Charles Spurgeon Commentary Numbers 9:3-7

"In the fourteenth day of this month, at even, ye shall keep it in its appointed season: according to all the statutes of it, and according to all the ordinances thereof, shall ye keep it. And Moses spake unto the children of Israel, that they should keep the passover. And they kept the passover in the first [month], on the fourteenth day of the month, at even, in the wilderness of Sinai: according to all that Jehovah commanded Moses, so did the children of Israel. And there were certain men, who were unclean by reason of the dead body of a man, so that they could not keep the passover on that day: and they came before Moses and before Aaron on that day: and those men said unto him, We are unclean by reason of the dead body of a man: wherefore are we kept back, that we may not offer the oblation of Jehovah in its appointed season among the children of Israel?" — Numbers 9:3-7 (ASV)

They were in a great difficulty. They were commanded to come to the Passover; they sinned if they did not come. But they had defiled themselves, either through accident or necessity, and if they came to the Passover in this state, they would be committing sin, so that either way they were in a difficult situation.

There must be someone to bury the dead. I suppose that these persons had fulfilled that necessary duty, and there had not been time for them to purge themselves from the ceremonial defilement involved in touching the dead; so what were they to do?