"...remember to set aside some of it as an offering to me. 20From the first batch of bread dough that you make after each new grain harvest, make a loaf of bread and offer it to me, just as you offer grain. 21All your descendants must follow this law and offer part of the first batch of bread dough."
Bamidbar (Numbers) 15:18-21
It’s explained in Midrash that whoever fulfills the mitzvah of (separating) challah (bread), it’s as if they nullified idol worship! How so? A person may feel that there is a need to daily plow, sow, grow, harvest, collect, winnow, mill, etc. grain to have bread to eat. This is, in a more expanded view, a metaphor for all manner of sustenance. Seemingly, a person may claim that it’s their merit and efforts within the natural order of things that bring the daily bread and this is done by getting involved in the sowing through baking process. Comes along the mitzvah of challah and proclaims that “the first batch of bread dough ” is given to G-d and not as charity but as an obligation and as a recognition that sustenance is not due to one’s strength but it’s really G-d, Who gives the power to succeed. And specifically through this, we bring blessings upon our homes. By doing this mitzvah, we nullify the appearance that natural occurrences in the world are somehow extraneous to G-d or outside of Him, i.e. not controlled by Him. I.e. we strip away that layer of reality that masquerades as forces outside of G-d's sovereignty. One could argue that, seemingly, gentiles also enjoy bread (sustenance) but without the added "burden" of mitzvah of challah. Seemingly it may be so, however, when Jews perform this commandment, they reveal and "blatantly" so, the truth that also in "natural" occurrences there is “ein od milvado”, that there’s nothing except for Him only. This concept isn’t necessarily demonstrated when we study Torah or perform mitzvahs but rather when we ‘re out in the world/field and reveal also there Emes Havayeh (the truth of G-d)
From the sichah of Sivan 26th, 5736 (1976)