2 Nephi 10:15

Wherefore, for this cause, that my covenants may be fulfilled, which I have made unto the children of men, that I will do unto them while they are in the flesh, I must needs destroy the secret works of darkness, and of murders, and of abominations;

I need to destroy all the secret evil works to keep my promises to people. I will destroy the works of darkness, murders, and terrible things.

So, to keep the promises I’ve made to people—the things I’ll do for them while they’re alive—I must destroy the secret works of darkness, the murders, and the disgusting evils.