Peter is given that authority (to forgive sins) by Christ Himself in the Gospels, which is why the emblem of the Pope is the two keys (gold for heaven and silver for earth).
I think the problem with relying too heavily on literally conforming one’s Christian life to the Epistles is that many of the accounts of things done by Paul or others relate to particular things that happened under particular circumstances, and were not meant to establish general policies or indicate any underlying doctrine. Thank goodness - I’m not sure killing people in church would be a real missionary draw, so to speak!
I’m not saying that Protestants don’t love God, by the way. It always amazes me to see how many people pass through life without ever giving God a second thought, and you’re right, people who do love to think about Him are certainly blessed. I can’t imagine, personally, never thinking about God, but it seems as if many people nowadays can. Although I think deep down inside, they know something’s missing.
It never actually says he killed them... it says they dropped dead. It doesn't say the Lord killed them either. They could have had heart attacks.
But Peter said, Ananias, why hath Satan filled thine heart to lie to the Holy Ghost, and to keep back [part] of the price of the land? Act 5:4 Whiles it remained, was it not thine own? and after it was sold, was it not in thine own power? why hast thou conceived this thing in thine heart? thou hast not lied unto men, but unto God. Act 5:5 And Ananias hearing these words fell down, and gave up the ghost: and great fear came on all them that heard these things.