Just a holy day like others. I went to Catholic school, and there were "feast" days. St. Theresa, St. Francis, lots of saints. Just days that gave those interested a cue to ponder that person's life and their contribution to those around them. I'm sure, in hopes that we would emulate the good they did. I know my Italian neighbors favored a few saints with Italian heritage. I think the whole St. Patrick's celebration was just an Irish pride thing that went commercial.