What does "to the extent that you give it" mean in context?

Question

What does the it refer to? What does the give mean?

Tell a devout Christian that his wife is cheating on him, or that frozen yogurt can make a man invisible, and he is likely to require as much evidence as anyone else, and to be persuaded only to the extent that you give it. Tell him that the book he keeps by his bed was written by an invisible deity who will punish him with fire for eternity if he fails to accept its every incredible claim about the universe, and he seems to require no evidence what so ever

-- Sam Harris

Answer 1

In English we use distance metaphors to express degrees of persuasion. If you are trying to persuade me of a fact and I am only partially persuaded I may say

• I am only persuaded up to this point, but not beyond.

• I am only persuaded so far but no farther.

• I am only persuaded to this extent.

The ‘point’ or ‘distance’ or ‘extent’ may be qualified with a relative or comparative clause which defines either the matter of which I am convinced or the quality of the argument which persuades me.

• I am only persuaded up to the point where you argue X; but you have provided no evidence for Y.

• I am only persuaded so far, that I accept X; but Y is not credible.

• I am only persuaded to the extent that you provide evidence. You provide evidence for X, but not for Y.

In your sentence, it refers to evidence: the devout Christian is persuaded only to the extent that you give evidence.

Answer 2

It refers back to "evidence":

Tell a devout Christian that his wife is cheating on him, or that frozen yogurt can make a man invisible, and he is likely to require as much evidence as anyone else, and to be persuaded only to the extent that you give it.

But there's also an omitted argument here, "to him":

Tell a devout Christian that his wife is cheating on him, or that frozen yogurt can make a man invisible, and he is likely to require as much evidence as anyone else, and to be persuaded only to the extent that you give that evidence to him.

It means that you'll need to present a devout Christian with evidence if you want to persuade him about matters unrelated to God.

The next sentence presents a contrast:

Tell him that the book he keeps by his bed was written by an invisible deity who will punish him with fire for eternity if he fails to accept its every incredible claim about the universe, and he seems to require no evidence whatsoever.

This says that he takes the existence of God on faith. In other words, he believes in God even without evidence that God exists. The paragraph as a whole presents this contrast in a negative light; the author is portraying the Christian faith as irrational.

_{Disclaimer: I'm not trying to express my own opinion here. I'm only trying to explain what the paragraph says.}