Warm yourself by the fire of the sages, but be beware in case you are burned by its embers; for their bite is the bite of a fox, their sting is the sting of a scorpion, their venom (literally "hiss") is the venom of a snake, and all their words are like flaming coals.
If the only point of this teaching is that the words of Torah sages can inflict pain, that point is established once they are likened to the fox’s bite, the snake’s venom and the scorpion’s sting—each one of which alone should be quite sufficient to deter anyone who might be thinking of tangling with a talmid chacham. Rabbi Eliezer could then have stopped after listing these three deterrents. Why then might he need to add the apparently unnecessary line about the sages’ words being “flaming coals”?
I have not found the following explanation in any earlier commentary, but in terms of moral guidance (mussar) it may have something to commend it. While fire has the capacity not only to burn but to inflict unbearable pain on anyone it touches, it has another quite different function. Fire also purifies. In the Torah (Numbers 21:23) we are taught, regarding the purification of vessels captured from the Midianites, that “everything that can withstand fire, you shall pass it through fire and it will be pure.” The same process is used even today for purging household utensils that have been used for preparing and serving leavened food products so that they may be used on the Festival of Passover when only unleavened food may be consumed (Shulchan Aruch, Orach Chaim 451). Bearing this in mind, we can provide an extra justification to the reference to flaming coals: while the words of the chachamim may be painful in an extreme, if they are understood and accepted by the person to whom they are addressed they will ultimately have the effect of refining and improving that person.
