I have a supervisor here in the San Antonio area that is a Notre Dame grad. The day after the Sun Bowl matchup was announced I asked him if he was going to go to the game, and warned him that El Paso's allotment of tickets would sell VERY quickly. The next day he came in to work shocked that tickets sold so fast. I pointed out El Paso's large Catholic population and reminded him that I warned him that tickets would sell quickly.
Growing up in El Paso, and growing up Mormon, I saw this phenomenon on two fronts: Catholics believing that God wanted them to place Notre Dame above all other schools, and Mormons will similar beliefs about BYU. I remember a Mormon missionary from Utah being appalled before a BYU/UTEP game that some members of the Mormon Institute of Religion (on Oregon across from the Baptist Student Ministry) were cheering for the Miners. I also remember thinking that he was an idiot. While my mom was one who cheered for BYU above everyone else, I only cheered for them when they played a P6, or, back when we were both in the WAC, a BYU win over a conference foe would help us in the standings. Now that they're in the Big 12 I just don't care.
The above is just to show that I understand the mentality of Notre Dame and BYU fans, even though I don't follow it. But I have more questions that I don't understand. Like why does Notre Dame get all of the Catholic love? El Pasoans wouldn't have shown this level of interst for DePaul, or Georgetown, or Villanova, or Loyola Marymount, or ... Also, is it only Catholics and Mormons that feel this way? I don't notice Baptists feeling like they must support Baylor, Methodist believing that God wants them to follow SMU, evangelicals don't appear to think that they must cheer for Liberty, or Oral Roberts, or ...
In the end I still don't understand why people feel that they MUST favor a religious affiliated university above all others. I can guarantee that God doesn't really care who wins on the field, court, diamond, links, pitch, etc. If He did, you'd see one or more of these schools dominating college athletics. They don't.