The name: מַשְחִית (destroying angel) is used by Makkas B'choros, and it destroyed the Mitzri'im who were Nichshal in Gilui Arayos, which is called: הַשְחָתָה נח ו יב destruction. There is a story in Sefer Shoftim about a famous No'ef (sinner). His name was Sis'ra, and he went to war against Klal Yisroel. He was killed by Yael who was known for Tz'niyus, like it says about her: מִנָשִים בָאֹהֶל תְבֹרָךְ שופטים ה כד she is blessed, like the women “in the tent”, i.e., Sara, Rivka, Rochel, and Leah. (Rashi).
She killed Sis'ra with the: יָתֵד peg of her tent, and the “peg” symbolized her Tz'niyus, since it holds down the Ohel. This was the victory of Tz'niyus over Pritzus, since Sis'ra was a big No'ef (sinner). (I told this to R' Schlesinger Shlita and he held this to be a great Pshat). And this is why in Mitzrayim we put: דָם blood on our: מַשְקוּף וּמְזוּזוֹת doorposts of our “home”. Our homes were protected from the: מַשְחִית destroying angel, since we had true homes, without Arayos like Mitzri'im.
