Do you have a verse. I'm not Mr. Answerman but I can give it a good shot. I will say there are a handful of problematic verses on this side of the tracks but they are significantly fewer than on the other side. I know. I've been there and I'm parroting all the verses that have troubled me for 30+ years. I don't get an explanation of what it is to be sealed with the Holy Spirit, what a new heart and new spirit means, how a Christian is born again, or what it means to be a "slave to righteousness". I throw out literally hundreds of verses (like my tagline) and all I get is, "Well, it's a mystery." All I hear is that we have "free will" although the Bible really doesn't state that.
What is He guarding that you have entrusted (past tense) to Him?
The Deposit of Faith. What else did Paul give Timothy? Paul layed his hands upon him and conferred to him the Holy Spirit, giving him authority to preach and teach, to bind and loosen, to forgive sins, and all of the other things that bishops were to do. Thus, the Holy Spirit will guard this power given to Timothy as well as the Deposit of Faith, the Apostolic Teachings.