Why do Jews, or at least religious Jews, have beards and not shave? Someone told me it was in order to get blessing. Is this the reason?
It is true that Jewish mystical sources discuss the beard in the context of blessing – either being a source of blessing or an expression of blessing. I am not aware of there being a rational explanation for this idea. On the contrary, it is in the realm of the esoteric.
But in any case, this is not the main reason religious Jews do not shave but rather grow beards. The main reason for prohibited shaving is simply that the Torah forbids it: “You shall not destroy the edge of your beard” (Lev. 19:27).
The Talmud (Mishna, Maccot 20a) interprets “destruction” as shaving with a razor. This prohibition also includes shaving with any implement which completely removes all the facial hair, but does not include trimming, or shaving with a scissors or other tool which does not provide the smooth shave provided by a razor (Sh.A., Y.D. 181:10).
This is the reason some observant Jews have short or trimmed beards as opposed to long ones. As long as they are not using a razor they can trim their beard. Similarly, some observant Jews achieve a clean-shaven look by using certain rabbinically sanctioned rotary shavers that cut not in a razor fashion but rather in a scissor action.
The most commonly accepted reason for the Torah’s prohibition of shaving with a blade is that it resembles the actions of ancient idolaters and was therefore prohibited for all times (Rambam, Avoda Zara 12:7). Another prohibition might apply with shaving if the man intends to adopt the appearance of a woman or to beautify himself (as in removing gray hairs), transgressing the injunction against cross-dressing (ibid 182:6).
For most of history and in most locales, Jews did not shave or trim their beards even in a permitted fashion. In modern times, having a long beard came to be associated with backwardness such that many who were swayed by the times, started trimming their beards accordingly. However, the more-stringently observant maintain the traditional custom of having a long beard, and some refrain from cutting or trimming the beard at all. This is either to emphasize the Torah Law or in consideration of Kabbalistic teachings.