R. Yonah: Mechitah is fear, like "Al Techas Mipneihem ¹ " (Yirmeyah 1:17). A Kesil fears his mouth like he fears his enemies, for his mouth is not in his control. He habituated his mouth to speak without investigation and thought. Therefore, his words constantly cause to him damage and stumbling. (He harms himself in many ways. He instigates quarrels with people, and reveals things that it is proper to hide them. This greatly disturbs his affairs and goals.

Malbim: Mechitah is breakage. Mokesh is before Mechitah. With his external lips he makes a Mokesh (trap) in which he is caught. With his mouth - internal speech with Chachmah - he completes the breakage. His lips trap his Nefesh to the pit (Gehinom), and via his mouth there is Mechitah also for his body. Hashem will punish him also bodily.