It’s a tricky task to explain the uncleanliness laws in our modern context. On one hand, being ritually unclean mirrored our fallen sin condition. Being human, we inevitably find ourselves stained with sin and unable to approach a perfect and holy God. On the other hand, the people of the OT could very easily have become physically unclean without meaning to. In this sense, it seems a bit unfair to associate physical uncleanliness with sin.
However, just like any spiritual analogy that God gives us, there are foundational truths to be found. The purification offering would cleanse both the effects of the physical uncleanliness as well as the sin issue. The people were to understand this from a deep, spiritual perspective so that they would approach God with reverence and humility.
In the NT, the word “unclean” applies much more to the spiritual aspects of one’s life. Jesus rebuked those who placed the ritual above the ethical heart issue. The Pharisees never moved in the same direction that the analogy attempted to teach. Jesus wanted them to look past the physical ritual and into their hardened hearts. In fact, Jesus many times broke this purification law in order to highlight the most important factor in our spiritual journey. It’s not that we need more discipline to follow the rules. We need a Savior to cleanse us permanently.
Now that Jesus has accomplished our freedom, we no longer have a list of clean/unclean activities. We have the Holy Spirit who guides and convicts us. Just as the Israelites were commanded to stay clear of things associated with death, we must lean into the Spirit in order to find self-control and wisdom with our daily conduct. If we are allowing things into our hearts and lives that are unclean by the Spirit’s conviction, He will give us the power to resist those temptations.