From HaYom Yom, from day to day, for the 8th of Cheshvan 8...
Mitzva is an idiom of Tzavta - "joining," "attachment."
Whoever performs a Mitzva becomes joined to the Essence of G-d - may He be blessed - Who issues that particular command.
This is the meaning of "The reward of a Mitzva is the Mitzva (itself)": His becoming attached to the Essence of the En Sof (the infinte one) Who ordained the command, is itself his reward.
THIS is the essence of Kabbalah, this is Jewish heaven. Becoming attached to the infinite, or rather attached to the Infinite. And how do you build this connection? Mitzvot, the commandments of G-d.
BS"D - בסיעתא דשמיא