God tells us to avoid all uncleanness as a manner of life. (Ep 5:3) Abiding in uncleanness is a work of our old man, the flesh (Ga 5:19-21), so we’re to put it to death. (Col 3:5-6) He calls us to holiness (1Th 4:7) in our entire being: spirit, soul and body. (1Th 5:23)
God’s definition of holiness exists only in Torah, Mosaic Law, where He defines what’s unclean, what defiles us, and how to purify ourselves and separate ourselves unto Him. (Le 11:44)
Becoming unclean is simply part of living in this world; even doing God’s will can make us unclean. (Le 12:2) The focus is on how we respond to our uncleanness. Do we pursue abominable things (Le 11:10), heedless of our filth (Pr 30:12), enjoying uncleanness (2Pe 2:10) and neglecting the purification process God has prescribed? (Is 1:16) Or do we obey Him and continually pursue fellowship with Him, cleansing ourselves of all filthiness of the flesh and spirit, perfecting holiness in the fear of God? (2Co 7:1)
We can try to spiritualize this away to mean whatever we like, but if our new man delights in God’s Law (Ro 7:22) we’ll look for ways to obey Him as well as we can. In ignoring God’s prescription for physical cleansing, why would we pretend to be aligned with His design for spiritual purity? Those who aren’t acknowledging all their filth, cleaning themselves up wholistically, purifying themselves and separating themselves to God as a manner of life, have no part in God’s kingdom. (Ep 5:5)
YHWH gave us laws on personal hygiene to keep us healthy, free of disease and infection, to teach us how to respect ourselves and others, and to give us insight into spiritual warfare. He calls us to live in purity, both in the flesh and in the spirit (1Co 6:20), pursuing holiness and faithfully cleansing ourselves of defilement and contamination because we belong to Him. (1Pe 1:14-16)
The physical dimension of uncleanness is tangible, and God’s prescription for it was written long before the sciences confirmed it’s value. Walking out physical holiness helps us understand the spiritual, to see how it works and ensure that we’re being cleansed of our sin (1Jn 1:7); both dimensions are essential in our walk with God.
Some might argue that the uncleanness referred to here is just sexual and spiritual in nature.
Moral/sexual is certainly a type of uncleanness, but the text says “all” uncleanness, of which physical uncleanness is certainly a type.
Fornication and purely sexual immorality are redundant; God is evidently saying there is more to uncleanness than the sexual aspect. Physical uncleanness becomes a spiritual/moral issue when it’s not dealt with properly, just like breaking any other law is a moral issue.
The physical concept is also found in texts such as “Having therefore these promises, dearly beloved, let us cleanse ourselves from all filthiness of the flesh and spirit, perfecting holiness in the fear of God.” (2Co 7:1) and “And the very God of peace sanctify you wholly; and I pray God your whole spirit and soul and body be preserved blameless unto the coming of our Lord Jesus Christ.” (1Th 5:23) God is evidently still concerned about the physical as well as the spiritual, just as He’s always been.