Tell them to go read their bibles. The book of Romans explains over and over that being a Christian does not require you to do anything. The only thing a Christian has to do is go to heaven.
I can't point to any verse, but AFAIK the only reason to go to a meeting is to fellowship with like-minded believers.
Going to heaven is not something we HAVE to do. It is what we are blessed to be able to do thanks thanks to Christ.
I would say that what we HAVE to do is treat other people in the manner that you want them to treat you. This is a hallmark of Christianity. Be kind to people, even when they are unkind to you. That way, you set an example for them, you become a representative of the Christian faith.
Matthew 7:12 Jesus Himself said......……….
"So in everything, do to others what you would have them do to you" .
Matthew 18:20 ........
"For where two or three gather in my name, there am I with there also". = Fellowship and worship.
Hebrews 10:25...…..
"Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching." = Obedience.