When tzaddikim perform a mitzvah they actually feel how it unifies their soul with G-d.
This, in turn, awakens within their soul a feeling of fear and awe of G-d, followed by a feeling of intense love of Him.
This, of course, is not the case with these who "feel not." - i.e. you and I.
Whether we feel it or not -
The soul DOES unify with hashem - When doing a mitzvah.
Even one who performs mitzvot on the level of a "fool" or "beast", (i.e. us) neither comprehending nor sensing the unity and holiness achieved and drawn down through his actions, even such a person, attains a union with the level of "beast" that transcends even that most lofty of levels (Daat of Atzilut).
The illiterate person's soul is illumined, e.g. on Shabbos, to the same degree as the tzaddik's. Their (our) punishment is therefore the same.