Abel

(Hebrew הבל Hei, Beth, Lamed, pronounced "ha-bel") Literally, "nonsense, futility, idleness, vapor, breath, vanity, to waste life on vain things."

One of the "sons" of Adam and Eve. A kabbalistic symbol with many levels of meaning. 

"And Adam knew Eve his wife; and she conceived, and bare Cain [Kayin], and said, I have gotten a man from the LORD. And she again bare his brother Abel [Habel]. And Abel was a keeper of sheep, but Cain was a tiller of the ground." - Genesis 4:1-2

"Adam in himself having become impure before conjugal union (fornication) with Eve his offspring was therefore impure, but Abel begotten in a state of purity after repentance was consequently pure. Thus we learn why the two brothers, Cain and Abel, were so dissimilar in nature and character." - Zohar

"And (through sexual achemy) Abel, he also (רָצוֹן ratsown, willpower) brought of the firstlings of his flock and of the fat (better said: quintessence) thereof. And יהוה Iod-Havah gave וישע salvation unto Abel and to his offering." - Genesis 4: 4

הבל הבלים אמר קהלת הבל הבלים הכל הבל - "Abel of abel, saith the Preacher, abel of abels; all [is] abel (futility)." - Ecc 1:2

"Light and darkness, White Magic and Black Magic, are mutually combating each other. Eros and Anteros, Cain and Abel, live within us in an intense battle, until by discovering the mystery of the sphinx, we grasp the flaming sword, and thus, this is how we become liberated from the wheel of the centuries." —Samael Aun Weor, Alchemy and Kabbalah in the Tarot

"We need the Solar Adam, the Abel to which the Bible refers, to be born within ourselves. In order to become immortal, the possession of the Solar Bodies is necessary." —Samael Aun Weor, Tarot and Kabbalah