Two reasons come to mind: 1) There's a long history of it. Gematria was a Jewish technique, then carried over to the early Christian community. There may have

Two reasons come to mind: 1) There's a long history of it. Gematria was a Jewish technique, then carried over to the early Christian community. There may have been reasons to keep it up as a matter of course, but as you said, with Nero it probably didn't matter: the dude knew everyone hated him. Not just Christians. 2) The purpose of Revelations was meant to comfort the current Christian community at the time by prophesying a future calamity with many parallels to the current calamity. The end of the world brings great destruction, yes, but there is vindication at the end of it all, and hence hope for the community. One thing to keep in mind about the nature of the "anti-Christ" is that it is the opposite of Christ in all ways. Christ was expected to come back at the end of days. So, too, then, was the anti-Christ. If the anti-Christ has never been seen before then "coming back" doesn't quite make sense, but it does make sense if the anti-Christ refers to Nero: he was a complete bastard in his first life, and he's so evil that he will come back at the end of days to persecute Christendom again.