How are they cleansed from defilement of a dead body?

Answer From The Annual Reading Schedule - Week 33 Notes For Numbers: Refer to Numbers 19 – It requires ashes of a red heifer which we don't have today and this is a seven day process. They would have been able to be cleansed and then perform it in the second month. Since I do not have a literal red heifer and I have been to funerals before, this is one of the reasons I do not slaughter and eat a literal lamb or goat for Passover. I am not sure that I qualify to do so. 2 Chronicles 30 shows that eating before being cleansed properly is doing something contrary to what is written – and I do not want to do that. Those who did that in 2 Chronicles 30 actually needed prayer to be made for them for atonement, showing that it was a sin.

For the other reasons why I do not slaughter and eat a literal lamb or goat for Passover, please refer to the reading notes for Week 16 answer for the question, 'Should believers today take a lamb on Passover and perform the Passover with all its' laws and ordinances, including the blood on the doorposts, etc., or not?'.

In response to that above statement about it being a sin to eat without having been cleansed with ashes of a red heifer, some might point out that, "we are cleansed in Messiah". I agree, we are cleansed in Messiah. However, does my faith in the cleansing from Messiah mean that I should make void the law?

Romans 3:31 - Do we then make void the law through faith? Elohiym forbid: yea, we establish the law.

The law still says what it says. We see Sha'ul (Paulus) [commonly referred to as 'Paul'] taking part with the ones doing offerings and cleansings in Acts 21 to show he was walking orderly and obedient to the law. In the same way, if the physical Temple was here with qualified persons (Sons of Aharon) (Sons of Aaron) to do the services required in Numbers 19, then persons who have touched a dead body, grave, etc. would certainly be cleansed as required with the red heifer ashes even today. Our faith that Messiah cleanses us does not give us a license to disregard the law. Also related, it appears in the future at some point people may be going through some kind of a cleansing process when clean water is sprinkled on them as prophesied in Ezekiel 36:25. Perhaps this is part of the cleansing process that happens for people who previously did not have red heifer ashes and such? I do not know for certain, but seems important to consider.