Chabad.org — English translation + Rashi
Torah Temimah points to Menachos 104b.
E-Daf.com — Menachos 104b
HebrewBooks / Shas PDF
English: Why is minchah distinguished that “nefesh” is said of it? The Holy One said: Whose way is it to bring a minchah? A poor person — I account it for him as if he offered his soul before Me.
Diyuk of the word nefesh — the unusual term signals special valuation of the poor man’s gift.
A poor person’s flour offering is valued as the offering of his very self. The Torah’s choice of the word “nefesh” rather than a more ordinary term for a person teaches that Hashem regards the modest gift of the poor as if the donor had offered his own soul.