I have been looking for this quote for some time. Apparently it is immediately after Brigham Young gives his statement about what your endowment is.
"Who has received and understands such an endowment, in this assembly? You need not answer. Your voices would be few and far between, yet the keys to these endowments are among you, and thousands have received them, so that the devil, with all his aids, need not suppose he can again destroy the Holy Priesthood from the earth, by killing a few, for he cannot do it. God has set His hand, for the last time, to redeem His people, the honest in heart, and Lucifer cannot hinder Him."
I find this quote fascinating because of its conclusion that the devil could no longer destroy the Holy Priesthood by killing a few BECAUSE thousands of people were now endowed.
Now I could ask any Sunday School or Priesthood class whether the priesthood could be destroyed by the death of only a few people and, after some thought, everyone would conclude that "yes" the priesthood could be destroyed by destroying only a few men. Anyone who dissented would not dissent on the basis that so many people were now endowed.
So there is something being taught here that we don't understand.
What does this mean? I don't know. But Brigham Young is one of the great prophets that has lived, and received extensive teaching directly from Joseph Smith.
Whatever it means, I think its meaning has long been lost to us. He is saying something about eternal matters so we can't simply reason out the answer - we can't use man's wisdom to determine truths known only to God. But we have the Holy Ghost - so we can certainly ask, seek, and knock and in time the Holy Ghost may reveal the matter to us. If we, being evil, know how to give good gifts to our children, how much more shall our Father in Heaven give good things to them that ask him?