Machatzis Hashekel is a Klalis (all important) idea in Torah, as it is “Lichaper Al Nafshoseichem” (to atone on the Soul). It is different than Teshuva because Teshuva is the complete breaking down of the person, while Machatzis HaShekel and the Aron haKodesh (Torah) are only halving oneself. The idea is not to be broken but to be a Keli for Ohr. Three examples for Machatzis HaShekel: 1) Half the person and half Hashem 2) Both halves are from the person [Torah vs. Mitzvos etc.], 3) The Z”A and Malchus in Atzilus. This third idea is relevant to us, as everything down here comes from us since Mattan Torah.
