Why is John's not going to church significant to this play?

Everyone in the Puritan community went to church; non-attendance in church within the Puritan community would single the Proctor family out and make them suspicious to those around them.

"Reverend Hale and the other court officials use private information for their public matters, such as information about the frequency with which they attend church and their belief in the existence of witches. The court officials investigate all aspects of the suspects' private lives. Under such intense scrutiny, these officials are able to find any information that may be may interpreted as evidence of guilt – not unlike the House Unamerican Activities Commission using everything from religion and sexuality to, in the case of the Rosenbergs, a discarded box of Jell-o as evidence of un-American behavior."