You are not a Christian. Where do you believe that Paul got his information from?
It is highly likely that Paul did actually persecute members of the Jesus sect. He mentions it in his letters and all it does is demonstrate that he not only didn't follow a living Jesus, but didn't believe those who said Jesus was the way to go.
However, we're dealing with a fundamentally different type of community structure and communication structure. If you've ever watched the film version of
Fiddler on the Roof, you'll know that things (like a guy playing a fiddle on a roof) are just the way things are.
For most of human history, and still today in some places, the idea of independence and individuality was virtually non-existent. If there was a communal tradition, rule, practice, etc., one just didn't question it. Their identities were based in a far more fundamental way than in the modern West and elsewhere could dream of. Those who lived around you weren't just "neighbors" in the modern English sense of the word, but were kin by blood or marriage (the word neighbor is etymologically a Germanic word that means pretty much exactly what the Greek word translated as neighbor in the NT means; those near you). Everyone's identify was defined by their relationship to this community (and by religious practices, language, etc.). Kenneth Bailey wrote two books in which he used his perspective gleaned from preaching in places which are very much like those of Jesus in many ways for exegesis. I don't really care so much about NT exegesis, but the communal aspect he observed that is reflected in the historical record is something I care very much about.
And it all adds up to this: connections between people were everywhere. One's name literally indicated one's ancestry or place of origins. Even without the internet, we can see form Pliny letter's, the recoveries of papyri mostly from Egypt, Tacitus, and from graph theory that social structure enabled a communication that was very much literally like the Wikipedia. That is, various nodes within the social network graph had degrees with high cardinalities. Everyone was connected to many, many other people such that communication flowed fast and openly and could be corrected.
Paul knew this. And he knew (and admitted) that he didn't have the claim to authorities other "pillars" did. So he downplayed the importance of any living Jesus, and told about his ecstatic (in the mystical sense) experience with YHWH. Whether he was lying or was actually driven into that state I don't know. But it also doesn't matter, as merely by indicating that he had persecuted the Jesus sect he tells us he knew of it. And in a region where a graph of weighted and directed communications lines between people/nodes has an incredible number of clusters, there is simply no way for one, like Paul, to claim he'd been with Jesus all along.
Nero blamed the Christians (according to Tacitus) for the fires. Pliny wrote to the emperor about how one should deal with these new "Christians". The earliest scrap of any copy of the NT came merely a few decades after it was written in a different country. Papias tells us of his questioning the disciples of Jesus' disciples. So in a century in which we have almost know evidence from anybody living in that century writing about anything, Paul's letters alone show how extended communication networks were. Also, given the distrust most people, including authors, had of written works relative to spoken, the fact that the gospels were written is indicative of a need to transmit information across long distances in a permanent form. The gospels are the only example of this kind of extensive documentation within the same century of an individual, because communication lines usually did not require more than the locally available oral sources and the now and again news from X location many leagues away.
Paul lived, preached, persecuted, wrote to, established, and even spent two weeks just with Peter all to communicate with other followers. The mere fact that admits to persecuting the sect is indicative of how futile it would be to ignore his earliest interaction with the sect. But even before he joined, he knew of it. After he joined, he claims to have been ordained as an apostle by god, but that's irrelevant. He knew before he was a member, he learned before he met with Peter, and he spent to weeks just with Peter. Whether he really experienced an altered state of consciousness or just lied I don't know. But whatever he says about having received info from god can be easily explained by the fact that, even in his letters, he was arguing with his superiors. Not focusing on Jesus' life or on the fact that Paul joined late is explainable through typical social mechanisms: the construction and maintenance of power structures with in a group.
He got his information from people. The famous lines you refer to are formulaic. They are like a prayer/pledge/oath/etc., in which one recites a memorized formula. Were I a believer in some god, I don't think it would be one that inspired formulaic expressions. Too tedious. And if he had to wait for a revelation, how did he know who to persecute? One can't persecute a group without knowing who the members are, and knowing who the members are entails knowing something about the group.
EDIT: Regarding graph theory and communications: there is
a site about one of the greatest mathematicians of the 20th century, Paul Erdös, which concerns graph theory and small world networks. Basically, it's a dynamic graph that assigns degrees of separation from Erdös. Thus, if you've worked directly with someone who worked with Erdös, you get an low (i.e., the distance is very small) Erdös number. Someone did the same for Kevin Bacon. The point is that it is graph edges, not nodes, that determine the flow of network communication and the dynamics of the flow (a regular graph has neither directions nor weights; a graph which one might use to model communications in the Roman empire during the 1st century would have both weighted and directed edges). Consider an old-school call list, where one person calls another, and that person has one specific person they call, and that person has yet another specific person they call, etc. In graph theory, this would be a number of nodes connected by directed edges, and no node (except perhaps the first and last) would be connected. Remove any node, and communication stops. A dynamic directed graph, however, is far different, It is adaptive, emergent, and not only increases communications but tends to ensure corrections of data flow.