Regarding the original post, I agree it’s quite a challenge and perhaps intimidating. Like, there’s this atheist, and you not drinking poison is the ONLY thing keeping him from being saved!
Well, if that were completely true, than it would be quite intimadating. However, I’m sure you know that there are plenty of other things keeping him from believing and repenting. Namely, sin, and lack of desire to believe in Christ. His heart is hardened. Now, it is true that many pious Christians were used by God to work miraculous deeds, which gave creedance to the truth of their message, and to the truth of the Gospel. And people were moved to believe the Gospel at seeing these miracles. And it feels like an impious, unfaithful cop-out to say “well, I shouldn’t do that, that was just for the early Christians.” Besides, you’re Catholic I suppose, so you can’t really say that, since miracles still occur occasionally according to pious Catholic belief.
So, my attitude towards that challenge would be this:
The miracles WERE INDEED performed, so he should recognize that, and believe, regardless of you’re drinking poison or whatever and living.
Also, and probably more importantly, remember the parable of the Rich Man and Lazarus. The rich man begged for Abraham to let Lazarus go back from the dead to warn his family to repent of their sins before they died. Abraham told him that they have prior witnessess (Moses and the Prophets) that they should believe, and if they don’t believe Moses and the Prophets, then they wouldn’t believe if someone returned from the dead (like a miracle).
Granted, that parable would be more direct to the Jews, but I think the principle towards us Gentiles would still apply.
So don’t let it get you down. Pray and witness to him, perhaps the Lord will grant him repentance, perhaps even motivate his will by granting a miracle in his presence for him to be amazed at!!
But He answered and said to them, "An evil and adulterous generation craves for a sign…;"