Arnold Fruchtenbaum points out that there are 116 verses in Leviticus devoted to the topic of leprosy. No other disease receives such an extensive treatment in the Mosaic Law. In Leviticus 13, specific instructions are given to the priests for identifying and diagnosing leprosy. To touch a leper was to become ceremonially unclean. Once identified as a leper, one was required to warn others on the roads by crying out, “Unclean, unclean!” (Lev. 13:45). Given the depth of the instruction here, leprosy was clearly a prevalent threat in the day of Moses.

Interestingly, Leviticus 14 instructs the priests on what to do in the event that a Jew was healed of leprosy. Again, Fruchtenbaum:

Yet, while Moses left the priesthood with these detailed instructions, it seems they never had an opportunity to put them into effect. Furthermore, though rabbinic writings contained cures for many different diseases, leprosy was not one of them….Interestingly, from the time of the completion of the Torah, meaning the completion of the Mosaic Law in Deuteronomy…there is no record in the Hebrew Bible of a Jew ever having been healed of leprosy.

(Fruchtenbaum, Yeshua: Vol. 1)

Miriam was struck with leprosy in Numbers 12, but this was prior to the completion of the Law. Also, her leprosy came and went quickly, thus it does not seem to meet the qualifications spelled out in Lev. 14. Also, Naaman was healed of his leprosy, but he was Syrian (Aramean), not a Jew; therefore, his healing would not have required anything of the priesthood. Jesus himself says that there were many in Israel afflicted with leprosy in the day of Elisha, yet only Naaman was healed.

Not until the days of Jesus does the Bible record an example of a Jew being healed of leprosy. The encounter is recorded in Matthew 8, Mark 1, and Luke 5 — its frequency signaling the episode’s importance in the life of the early church. After healing the leper, Jesus commands him to go directly to the priests to begin the process of cleansing prescribed in Leviticus 14.

All three Gospel accounts tell us something Yeshua said that is very significant: He stated that when the man presented himself to the priests to perform all of the rituals Moses had commanded, it was to be for a testimony unto them, “them” obviously referring to the priests. There was a purpose to this miracle beyond it being an act of compassion toward the man; it was more than a piece of evidence of Yeshua’s ability to perform great healing. The cleansing of this leper was to testify something to the priests. Clearly, by the end of the eight days of rituals, they would have known it was Yeshua of Nazareth who had done the healing.

(Fruchtenbaum)

Jesus heals the leper as a declaration of his identity as Messiah. Historically, the rabbis considered leprosy an outward sign of an interior problem. With this healing, Jesus announces his ultimate purpose: to heal us of our internal problem, our heart and soul problem: sin.