The Symbol of Hashems's Oneness and Mastery
Aleph, the first letter of the Aleph Bet, and in my opinion the most enigmatic and esoteric.
The Aleph in it's essential nature always points to the Oneness of Hashem. That in Him there is absolute agreement and unity, and no disparity between His thoughts, speech and action.
Aleph symbolises the One and Only, the Eternal, the Omnipotent Hashem.
The Midrash teaches that G-d himself addresses Aleph, saying that Aleph stands at the the head of the Aleph-Bet like a king, "You are one, I am One, and the Torah is one", and that He pledged to use Aleph as the first letter of the Ten Commandments.
Aleph represents the one Devine, unchangeable Torah, the Thought of Hashem, the repository of all wisdom. Concealed in the Torah, in the combinations, crowns and shapes, are the laws of physics and metaphysics, music and mining, psychology and ethics.