I saw a few books mentioning Shedim (demons) and even the Gemara mentions them. I always thought that demons was a primitive superstition but then, it seems our sages believed in them! Maybe I have a misunderstanding of what Shedim are
Shalom! There are many things in life beyond that which is seen by the naked eye, and among them are what we call malachim (angels) and sheidim (negative angels). As opposed to other religions, Judaism believes that they have no free-will, are not independent, and are just robot-like messengers doing the will of God. This can include germs, viruses etc..
The Talmud mentions beings called sheidim, but also states, “one who worries about them- they bother him, while he who doesn’t worry about them, they don’t bother him” (Psachim 110b). Similarly, among the rishonim there are different opinions.
The Rashba, for example, talks about them but the Rambam whenever he must, explains the concept in rational terms (e.g. Hil. Rotze’ach 12, 5). Nevertheless, all agree that man and God, and no other forces, run our lives. Only we and God have free will, and accordingly we’re not allowed to believe in superstitions or the like. Many point out that certain powers that may have existed, aren’t found any more today in our countries (e.g. Magen Avraham 173, 1), and Rav Kook adds from the kabbalists that in the Holy Land of Israel, all the more so, that one need not worry about sheidim.
With Love of Israel,
Rav Ari Shvat