Who was St. Patrick and why is he celebrated?

(CBS News) Saturday's St. Patrick's Day Parade in New York is taking place one day before the official holiday honoring Ireland's patron saint. But what will all the revelers across the country be celebrating?

Some say St. Patrick eradicated snakes from Ireland and others do not have a clue.

Jim Gallagher, the barman at Molly's on Manhattan's east side, said St. Patrick's Day is "hectic." He would be surprised if many of his customers knew the history behind the holiday and said that half of them don't know who the holiday's patron is, and just come along to his bar to be with friends.

Jon Sweeny, a good Irishman himself, wrote a book about St. Patrick, who was born in 389 and was actually a Roman citizen of Britain.

"It doesn't surprise me at all that people at a bar on St. Patrick's Day don't know who Patrick was. I think, in fact, if you ask them, nine out of 10 would say he's a great Irishman or nine out of 10 would say he brought Christianity to Ireland - neither of which is true," said Sweeney. "Patrick didn't bring Christianity to Ireland. Christianity was already there. All of the experts agree on that now, but what he did was he, he organized it, he inspired it, he expanded it."

More than its religious roots, many associate the holiday with the St. Patrick's Day Parade down New York's Fifth Avenue.

St. Patrick's own journey included six years as a slave, when he found his faith, and then he spent decades formally studying it before returning to Ireland as a missionary.

"He sort of famously drove paganism out of Ireland, which is that sort of metaphor of the snakes, you know? There are no fossil records of them ever having been snakes, but the symbolism, the symbolism works," said Sweeney.

March 17, the day of St. Patrick's death, is known as his feast day, a celebratory term for when, Christians believe, his soul went to heaven, but, for most celebrators, they may be embracing history or perhaps just grabbing a green beer.

For Seth Doane's full report, watch the video in the player above.