Hilchos Lashon Hara, Opening – Negative commands (5)
The speaker also transgresses the negative command of (Devarim 8:11), “Be careful lest you forget Hashem your G-d,” which is a prohibition against pride. For since he is mocking his fellow he probably considers himself wise and an important person, and if he realized his own shortcomings he would not mock his fellow. Thus, Chazal say in Sotah (4b) that the sin of pride is exceedingly harsh, and that if one transgresses this sin his dust will not stir at the resurrection of the dead, he is considered like a worshipper of stars and constellations, the Divine Presence wails over him, and he is called an abomination.
In particular, if the speaker of lashon hara glorifies himself he certainly transgresses this negative command and in addition, the sages say he is cut off from the world to come, saying (Yerushalmi 2:1), “Someone who is glorified through the calumny of his fellow has no portion in the world to come.”