Lev. 15:31
Thus, you shall separate the children of Israel from their uncleanness; that they die not in their uncleanness when they defile my Tabernacle that is among them.
It would be a mistake to equate set-apartness (or holiness) with purity or cleanliness. YHWH calls all His people to be separate from the secular world. Yet there are several ways His people can become unclean.
In Leviticus chapters 12-15, YHWH gives His people instructions for how to keep themselves pure to enter a Set Apart place.
Some of these instructions can only be followed when the Mikdash is present. For example, while there is no Tabernacle or Temple, sin offerings (Lev. 12:6-8; 14:29-30) cannot be performed. Additionally, the infection of the skin, clothing, and houses (Lev. 13-14) was tied to the existence of the Mikdash.
On the other hand, though there is no standing Temple, respecting the Sanctuary (Lev. 19:30; 26:2) can still be practiced today. YHWH declared through His prophet Ezekiel that even in exile, He would be to His people as a little Sanctuary. Eze. 11:16.
Through Isaiah, He said that He would be a Sanctuary for those who trust in Him. Isa. 8:14. He also said that He would dwell with those who humble themselves before Him. Isa. 57:15
I dwell in the high and holy place, with him also of a contrite and humble spirit.
And again (66:2)
to these will I look, even to him that is poor and of a contrite spirit.
As the Psalmist also declared, His Presence is with those whose hearts are pure. Psa. 24:3, 4a
Who will ascend into the hill of YHWH? or who will stand in his holy Place?
He who has clean hands, and a pure heart.
In other words, His promise to those who accept His kingship is that they would become His Temple—a place for His rest.
This is why the apostle Shaul wrote to the Corinthians “Do you not know you are the Temple of the Mighty One?”. 1 Co. 3:16. And again “Your body is the Temple of the set-apart Spirit”. 1 Co. 6:19.
This is also why he wrote to the Ephesians that they were being built into His set-apart habitation. Eph. 2:20-22. Coming together with other set-apart ones can create a Set Apart place. Mat. 18:20.
Abstaining from all forms of physical contact for one to two weeks postpartum is one way to practice purity today.
Not touching the carcass of a deceased person or animal is another. Not drinking standing water with a carcass in it, not touching a human bone or a grave, not eating an animal found lifeless, and not touching anything that a person who has become unclean has touched are all ways to practice purity.
Most of these things would prohibit entry into a Set Apart gathering place until the evening. A couple instanced would prohibit it for a week. The longest period a person could be impure for the purposes of entering into a Set Apart gathering place would be eighty days, or flowing issues, whichever lasted longer.
2 Cor. 6:14-18
In his second letter to set apart ones living in Corinth, Shaul implored them to refrain from fellowship with the unbelieving world. In doing so, he used passages from the books of Leviticus, Isaiah, Ezekiel, and second Samuel.
When he used the word ‘unclean’ in 2 Co. 6:17 (cf. Isa. 52:11), he was referring to a practiced behavior. He used this same term in a list of what he called the “works of the flesh”.
Gal. 5:19
On a handful of occasions in his letters, Shaul used a similar list of evil practices, in which uncleanness is named. 2 Co. 12:21; Eph. 4:19; Eph. 5:3, 5; Col. 3:5.
He even used this term in Romans 6:19, when speaking of our past bondage to sin—that is, to lawlessness.
We can conclude, therefore, that while the camp in the desert had to be pure because YHWH’s presence was among them (Lev. 15:31; Deu. 23:10-14), YHWH also desires His people to be clean from within.