the certainty you have is based in faith not fact
how do you know that? I share the fact of my experiences with others and most toss it away with a snort of derision. I am part of the collective proof.
most demand very specific proof of what I'm saying. I can't reproduce a transcendent, divine experience given only to me....how would I do that?
I can certainly lead others to God so that they can experience their own revelations of his reality.
at this point I typically get the canned "I feel sorry you" or "you make me sick" or "you're mentally ill".....insert whatever canned ad hominem.
I'm under no delusion I can convince even a single atheist on this board of what I've experienced in Christ, but they're not who I'm speaking to....they're just the only ones posting. So I'm polite and discuss where discussion is temporarily allowed.
The folks that what to know the risen Christ seek him out proactively because their hearts yearn for him....some come to me privately for help and I help where I can.