A Metzora represents someone who is on a spiritual decline. He therefore, becomes impure with a mark, a “Nega”and is sent out of the camp, where he reflects on his behavior and actions, changes his ways and becomes a Bal Tshuva. Interestingly, the Nega is an extremely low thing, yet it brings the person to the greatest of heights. Similarly, the rabbis say, that when Tshuvah is done out of love and from the depths of your heart, it can actually transform all your sins into good deeds. Since you are repenting from the core of your Neshama, you are, therefore, connecting yourself to Hashem where future and past equally exist. This actually enables you to change the past.

לקו״ש כז-ב