“A man may be a heretic in the truth; and if he believe things only because his pastor says so, or the Assembly so determines, without knowing other reason, though his belief be true, yet the very truth he holds becomes his heresy.”
John Milton wrote this in his Areopagitica. He was talking about the chance that books classified as 'heretics' couldn't be published under the decree issued by the English government at that time.Thus he said what he thought about heresy. Perhaps later I will discuss about this, I mean, in another post, but for now I'd like to note how he stressed the importance of reason in men, based mainly on that quote.
A man's heresy – in this case his failure to have true faith or conviction– does not depend only on what he believes in, but why he believes it. If somebody believes in something just because 'his pastor says so', therefore based on what people say to be true, then the basis of his believe is wrong, regardless the veracity of what he believes in.
By this statement he stressed that men must use their reason to determine the right or wrong, instead of blindly believe in what they are taught to be right. In Areopagitica, he also quoted the Bible itself, that says:
“Prove all things; hold fast that which is good.”
It is not wrong to question what someone believes in. It is not a sin to doubt your religion. On the contrary, when you have proved “all things”, you will have stronger conviction on what you believe in.