In the book of Leviticus, God spent plenty of time instructing the Priests on how to properly give a burnt offering. For some reason, Nadab and Abihu ignored those instructions and offered a strange incense fire to God. He didn’t approve (of the disobedience), and allowed that fire to devour the bodies of those two.
I know I’ve been disobedient. I have not always obeyed the commandments of God. I fancy myself a good Christian, but I’m probably fooling myself more often than not. Any day now, God could take his hand and just erase me. He could, but I trust that because of my salvation and repentance, he forgave me, even before the sin was committed.
He still has the ability to just wipe mankind from existence, though.