The Torah teaches us that following the long introspective process that a former metzorah has to undergo there is a semi bizarre ritual he must participate in before his atonement is complete. The metzorah must shave all of his hair. All of it - head, eyebrows and all. [See Vayikra 14:8-9]
What message about reformation could Hashem be sending us by including this law ?!
It’s all about growth.
There are three components to the offering of the metzorah. There is the pine branch and the bird which is slaughtered [Vayikra 14:4-5] which represent the haughtiness and gossiping that the sinner engaged in which is what landed him as a metzorah in the first place. Next, there is the hyssop and worm-dyed wool and live bird which represent what he should be from now on – humble like the lowly hyssop and worm, despite being alive like the bird. But neither of these two stages represents what the baal teshuvah needs to avoid a relapse.
That’s where the hair comes in. Literally. When you have gone without any hair at all – you will be more attuned to its presence and rate of growth. It’s been said that life is like a downward escalator – if you are not going up – you’re going down. What may have been a solid conviction to remain humble the week after his offerings may turn into a distant memory a few years down the line. What is a more constant reminder for the former metzorah, however, is spiritual growth. As long as he is growing in his avodas Hashem then he will be reminded not to backslide into the arrogance and selfishness that caused him to deserve tzaraas.
While we are not recovering metzoraim (Thank G-d) this lesson is equally applicable to us. This is probably why hair continues to grow even after most things have stopped. As an “adult” we are no longer getting taller and our shoe size is no longer changing. But hair keeps growing to signify to us that there are aspects of our life that we must constantly seek to grow in.