10His disciples say unto him, If the case of the man be so with his wife, it is not good to marry.11But he said unto them, All men cannot receive this saying, save they to whom it is given.12For there are some eunuchs, which were so born from their mother's womb: and there are some eunuchs, which were made eunuchs of men: and there be eunuchs, which have made themselves eunuchs for the kingdom of heaven's sake. He that is able to receive it, let him receive it.
Any church that wants to last more than one generation is going to have a problem with this line. Indeed, the proto-orthodox church had to brand ascetic sects as heretical in order to continue receiving tithes after the initial converts were made. The greek for the word in question is εὐνοῦχος (eunouchos) and it is rooted in the word for bedroom, which makes sense in that men with large harems would use castrati to guard their women, thinking that the lack of testes would render these guards uninterested in sex with their charges. This evidently was not the case (see Ulpian in the Roman Digest of Law or Hammurabi's Code.) In any case, it's pretty clear that Jesus is talking about someone doing something painful or difficult to himself to make it hard or impossible to procreate. Even clearer is the message that it's better not to get involved with women at all, but it's undeniable here that he teaches that someone who is dedicated to the Kingdom of Heaven will not get married.