A person who resolves on New Year's Day to attend church more regularly during the New Year, hits up church every Sunday in January, then loses steam by about February or March. He or she may recover enough momentum to make it church on Easter Sunday but probably not very often after that.
Man A: You comin to my pre-game dis afternoon?
Man B: Yeah, after church.
Man A: After /church/? Hell's up with that?
Man B: My woman? She's a January Christian. Happens every year. I give her to March, though. She'll be out when the sun comes out.