To put it plainly, religion is communism biggest enemy, people of who have religion doesn't need to follow a communist government. Much like religion is even capitalism biggest enemy, since it condemns on consumerism and material values.
But communist go even lower, they proclaim themselves protectors of the poor people, the unfortunate, the gays, the heretics, the womyn, funny enough with the exception of Russia itself. They use lowly tactics and disinformation, accusing the opposition of exactly what they practice, they promise to defend the poor wageslaves but instead practice the most savage capitalism, they promise to govern with the people for the people, but they end up with the most corrupt autocratic despotism.
So they knew religion imposes a large barrier restriction, specifically the americas, where they couldn't spread their influence just as likely, so they infiltrate alternate churches to try and seed their ideology.
eg. brazilian who experienced first hand their nasty tactics and hopefully downfall.