Christian, did you know that you can lose your reward in heaven?
I didn’t say that you could lose your place in heaven: once a person is saved by Jesus Christ that is assured. But the reward, presumably the amount and/or the sort of reward it may be, can be decimated according to John the apostle:

Watch yourselves so that you don’t lose what we have worked for, but you may receive a full reward. (2 John 8, HCSB).

What was he talking about? False teachers were in the vicinity in which the recipient of the letter lived. They were seeking lodging while they propagated their false doctrines. John warns her not to receive them into her home lest she become guilty of assisting the propagation of error. To even give them an encouraging greeting was wrong (vv. 10,11). To do so is to “share in [their] evil works” (v.11).
Christians have not always adhered to these commands. They have bought and even distributed materials purporting to be Christian (without recognizing their falsity), they have literally opened their doors to Jehovah’s witnesses (while the latter held a convention in their city—I know personally of such a case), they have placed their books in waiting rooms, etc.
And, of course, there is always the possibility of one who thinks he is a believer because he attends a Christian church (but really isn’t) becoming influenced to “go beyond” what he has been taught by accepting false, damning beliefs, by such close associations (cf. v.9). To do so, is evidence that one never belonged to the truth after all.
So, keep away from false teachers because the effect upon yourself and upon others you may be trying to bring to Christ—recognize the danger of not heeding John’s words. Are you supporting the propagating of error in some way?