Leviticus chapters 11-15 deal primarily with being "clean" and "unclean". God details what causes a person to be "unclean" before the Lord, unfit to stand near God's presence. Deliberate actions can cause uncleanness in God's people, but what is striking about these chapters is how pervasive, how commonplace uncleanness will be in Israel. The ordinary course of life will inevitably cause the Israelites to be unclean, unfit for God's nearness, in need of cleansing.
Based on these chapters, it would be impossible for a person to be permanently clean before the Lord. This, indeed, is the point. Mankind is dirty before the bleached-white holiness of God. This pollution is not only on the basis of deliberate sins, not only the result of scandalous acts of depravity. To be unclean is to be normal, to be human. In our pluralistic culture, we sneer at the standard of ritual cleanliness presented in these four chapters. But it's actually easier to be "Levitically clean" than to be spiritually clean before God. By God's standards, every human, walking a "normal" course of life, is unclean, dirty, unfit, unworthy, in need of cleansing.
This background makes the New Testament sing.
And behold, a leper came to him and knelt before him, saying, “Lord, if you will, you can make me clean.” 3 And Jesus stretched out his hand and touched him, saying, “I will; be clean.” And immediately his leprosy was cleansed. Matt 8:1-3
But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God. 1 Cor. 6:11
let us draw near with a true heart in full assurance of faith, with our
hearts sprinkled clean from an evil conscience and our bodies washed
with pure water. Heb. 10:22
that he might sanctify her, having cleansed her by the washing of water with the word,
Eph. 5:26
For whoever lacks these qualities is so nearsighted that he is blind,
having forgotten that he was cleansed from his former sins. 2 Peter 1:9
The Lord Jesus has cleansed us, rendering us clean in the sight of God. No matter how unclean we are in our past or present sins, in him all of our guilt and shame is washed away.