parashat bereishit - What was Hevel (Abel's) sin?

The Arizal says that Hevel was reincarnated many times to purify his sin. What was his sin?

Answer

See here as a translation from the Arizal:

Cain and Abel also damaged [reality]. [Not only Cain but also] Abel "gazed and damaged".

According to the Sages, when Abel offered his sacrifice to G-d, he gazed upon the Divine Presence and therefore became incurred the death penalty (which is why it was divine providence that Cain killed him). Gazing upon the Divine Presence means experiencing divine consciousness for selfish intentions. The individual considers himself an independent agent who may rightfully pursue his own satisfaction. Having chosen to sunder himself from G-d, the source of life, he forfeits life - even if the object of his satisfaction is none other than the Divine glory!

This is the mystical meaning of the phrase: And G-d paid heed to Abel and his offering (Gen. 4:4). We would have expected this phrase to read: "And G-d paid heed to Abel's offering." The meaning of G-d turning to Abel here is that He allowed him to gaze [on the Divine Presence].

Abel should have demurred, aware that it doing this would cause him to experience G-dliness as one separate from it. Indeed, when Moses realized that the burning bush was a revelation of G-d, he "hid his face, for he was afraid of gazing at G-d." (Commentary of Rabbi Shalom Sharabi on Ex. 3:6.)

Raises the next question of where the reference is to "According to the Sages" but that is another question.