Each themer used a different definition for "Cardinal", and describes their behaviour in a sinful way:
6A A Christian cardinal marries (performs a marriage ceremony for) multiple people in a CHURCH
11A A member of the ARIZONA Cardinals might take a chip shot (kick the ball accurately but with less force than normal) from a pistol (an attacking formation)
21A A member of the STLOUIS Cardinals might hack (swing awkwardly to hit) a bomb (home run)
25A On a painting CANVAS, the colour cardinal (a shade of red) might be used to depict the devil
12D A female cardinal bird lays eggs in a NEST (with the help of their mate who has almost certainly never been married)
Glad you were able to finish the crossword regardless!
I had the same experience as Mike. I definitely enjoyed the solve but was scratching my head about the theme clues. The explanation is very helpful. Thanks!