Read Leviticus 11-18
"Cleanliness is next to Godliness." It will surprise many to discover that the quote is not in the Bible. Most sources attribute it to an ancient Hebrew saying and has appeared in many forms ever since. The first known similar expression in English comes from the writings of Francis Bacon in 1605: "Cleanness of body was ever deemed to proceed from a due reverence to God." Then, in 1791, John Wesley wrote, "Slovenliness is no part of religion. 'Cleanliness is indeed next to Godliness."
Imagine, several millions of people traveling in primitive conditions on foot. There are no hospitals, no Center for Disease Control, and no awareness of things like germs, contamination, etc. God demonstrated His special care for His people by giving them specific, practical instructions as to how to care for and protect themselves.
The purification was not limited to the physical body. Laws regarding moral behavior were included. Note the terms in Chapter 18 that God used for unlawful sexual behavior-depravity, abomination, perversion, iniquity. Sex outside of marriage is not okay with the LORD. Just as those who do not follow physically cleanness will suffer, so shall those who practice moral impurity.
Do not miss how God provides for spiritual cleanness in the middle of all these laws regarding purity. Instructions for the Day of Atonement are found here. Only the High Priest could enter the Holy of Holies and that once a year, only on this day. The description in chapter 16 is where the term "scapegoat" is derived. The High Priest laid his hands on the goat; symbolically transferring the guilt of sin, to the animal would die in the place of those who sinned. The blood was sprinkled on the Mercy Seat. This was the lid of the Ark of Covenant that contained the two tablets of the law. In other words, when God looked upon the demands of the law, He saw them through the blood that atoned for their sin.
That is exactly what Jesus did on the cross. He died in our place. His shed blood paid for our sin once and for all. At that very moment God ripped the Holy of Holies curtain in the temple from top to bottom. No longer would there be a need for sacrifices for sin. No longer would there be a need for a priest to intercede.
"For there is one God, and there in one mediator between God and men, the man Christ Jesus, who gave himself as a ransom for all..." (1 Timothy 2:5)
So, is cleanliness really next to Godliness? Yes...inside and out.
"The fear of the LORD is clean, enduring forever, the rules of the LORD are true." (Psalm 19:9)