I was listening to a podcast that was talking about psychics who had experienced a faith crisis when they realized that they didn't really have supernatural abilities, just good insights into human behavior. One said the big revelation for her was when she realized that everybody is concerned about the exact same things but but we all think we are unique. When the psychic figure outs which one of those (health, work, love, family...) is on the person's mind and gives them a few general statements their brains fill in the specifics and they come away thinking the psychic made precise observations and predictions, even though that never actually happened.22 Verily, verily, I say unto you, if you desire a further witness, cast your mind upon the night that you cried unto me in your heart, that you might know concerning the truth of these things.
23 Did I not speak peace to your mind concerning the matter? What greater witness can you have than from God?
24 And now, behold, you have received a witness; for if I have told you things which no man knoweth have you not received a witness?
For some reason that made me think of Oliver Cowdery. Imagine that you are an intensely religious person who has faithfully sought out a charismatic person who you believe might be your direct connection to God. Wouldn't you pour out your heart to God to know if it was true? And then if you received comfort about it wouldn't that be manifest in a change about how you treated that person? Might you even say that to them in so many words, even if you didn't tell them the whole story?
Now consider how non-specific this is to Oliver Cowdery. In fact, if someone said the same thing to anyone on this forum when they were still believers I bet you would have been able to think of a time that revelation would apply to you.