Not just any church of course, but a Mega-Church.

1. Obama uses Rick Warren as an endorsement to escape his association in public minds with the so-called "reverend" Wright:

“looking forward to going back to Saddleback with his good friend Pastor Rick Warren.” Obama spoke at Saddleback in 2006.

2. McCain gets to publicly show that he is not averse to (so-called) Christian political churches, which he has criticized in past.
3. Rick Warren, Mr. Hireling and his "Purpose Driven Church"(merchandisers), gets to increase his publicity and no doubt a huge intake of "tithes and offerings" (and 5013c IRS laws will not prevent, since it is bipartisan) for his corrupt church, which Jesus and the apostles would not recognize any more than a Roman Catholic Mass.

All in all, this is theater and corruption, religious and political leaders, like the Pharisees and Herodians getting together (who persecuted apostles, as Jesus warned), but no one dare say so.