[Read: Leviticus 13:1-46]
The Difference Between Leprosy-Like Ailments and Leprosy
God gives Moses instructions on how to identify true leprosy from false leprosy. True leprosy is “deeper than the skin,” while false leprosy is only on the skin; the former finds its place of origin within the leper, while the latter is merely an external form of sickness. And it is only the Word of God that reveals the nature of the leprous symptoms exhibited in those within Israel. Apart from God’s Word, would the Israelites be able to distinguish true leprosy from false leprosy? Without God’s Word, would they be able to properly treat either form of sickness? It is God’s Word that reveals true leprosy, false leprosy, and how to treat each properly. Apart from the Word of God, the Israelites would not be able to properly distinguish one from the other, and they would not be able to properly treat each. The lesson here is immense when we consider that leprosy is a type of sin, for in light of this fact we see that there are all forms of skin sicknesses (e.g. true leprosy and false leprosy) which may cause an individual to be unclean; however, there is one form of sickness that goes deeper than the skin, and there is another form of skin sickness that goes no further than the skin itself.
Corresponding to these two types of skin sicknesses are two forms of sinfulness, viz. (i.)sin that goes deeper than the skin, exposing the heart that is fixed in its rebellion to God and His Law and, therefore, proceeds from an unregenerate heart of stone; and there is, on the other hand, (ii.)sin that proceeds from the remaining corruption residing in a believer who is, nonetheless, a regenerate child of God. The sin of an unbeliever and the sin of a believer are both equally sinful; the sin of the unbeliever and the sin of the believer, likewise, both separate those who commit them from the Body of Christ (although in very different ways); and both the sin of the unbeliever as well as the sin of the believer can only be identified and treated by the Word of God. Where the difference lies is in the origin of the sickness, which indicates its true character. There is a difficulty in differentiating between one and the other, no doubt; however, it is possible to state with certainty what sins are indicative of a reprobate heart and what sins are indicative of a regenerate heart that is struggling with sin. For example, false beliefs concerning the foundation of the Christian faith cannot be held by a person who is truly regenerate (e.g. salvation by works, salvation by faith and works, Unitarian monotheism, polytheism, etc), and there are certain orthodox beliefs that can only be held by a regenerate believer (e.g. the Trinity, justification by faith alone, Monotheism, the life-death-burial-and-resurrection of Christ Jesus, etc).
The Word and The Priest
We know, then, that it is the Word of God that properly distinguishes one form of leprosy from another and, via implication, one type of sinfulness from another. The question to be asked is: Who applies this Word to God’s people? Who is it that examines the heart and responds appropriately with the Law and the Gospel? In this chapter of Leviticus, the answer is clear: It is the Priest who examines supposed cases of leprosy, applying his knowledge of the Word of God to the situation, identifying the sickness as true or false leprosy and, consequently, responding appropriately by the use of God’s Law and/or Gospel. And this Priest is Jesus Christ, our Lord, who by His Spirit applies the Word to us, examines our hearts in light of His Truth, and convicts us of sin and of righteousness. As Christ told His disciples in John 15:3, “You are already clean because of the Word I have spoken to You.”
In salvation and sanctification, the Lord Jesus Christ is our High Priest who (i.)died once for all for the sins of His elect people, and (ii.)ever lives to intercede on their behalf. Perfection will not be ours until we we are glorified, but we can seek the Lord now in our time of need and receive mercy and grace. Our High Priest is not unable to sympathize with our weaknesses; He was tempted in every way that we are, but was yet without sin.
 Cf. Lev 13:3, et al.