Faith is a major component of Christianity. For example, Jesus says to Thomas“Because you have seen me, you have believed; blessed are those who have not seen and yet have believed.” So Thomas, who knows Jesus is resurrected because he has seen and felt him, is less blessed than those who simply believe (but don't know). Likewise, though God could easily get a bunch of converts by showing Himself, doing that would lose the faith aspect.
Don't go being smart and saying that you by definition have faith in things you know -- Christians don't mean this definition of faith, nor is it necessarily true. You can also set up certain experiments you personally know by the laws of physics won't hurt you, yet if you measure your fight or flight response will realize that you "believe" they are dangerous despite knowing they are not. Or compare how you feel about roller coasters compared to other activities you know to be of comparable likelihood of injury.
Another thing is that it is the dogma of many Christian denominations, that faith is a prerequisite (for some the only prerequisite) to salvation. Thus I claim that for Christians, faith is a more praiseworthy trait than knowledge of the same thing as a fact. A Christian who says that they know God exists, is signalling a very strong faith and most definitely not that they don't need faith because they have factual knowledge.
Now although Christian, Jew, and Muslim all claim to follow the same God of Abraham, I can't say for sure how this applies to your Jewish friend. The Torah also has "thou shalt not put God to the test", and various bits praising faith, plus they also need something that predicts that God doesn't go show Himself to the world population. Anyone here know whether for Jews it is better to believe in God than to know God exists?
Your entire post is basically redefining words. You specify that Christian "faith" is really "faith in things that cannot be proven". A Christian who "knows" is really "one who feels extremely confident". And "belief" is now "fight or flight response". These aren't the concepts the original post is about.
I recently spoke with a person who... it's difficult to describe. Nominally, she was an Orthodox Jew. She was also highly intelligent, conversant with some of the archaeological evidence against her religion, and the shallow standard arguments against religion that religious people know about. For example, she knew that Mordecai, Esther, Haman, and Vashti were not in the Persian historical records, but that there was a corresponding old Persian legend about the Babylonian gods Marduk and Ishtar, and the rival Elamite gods Humman and Vashti. She knows this, and she still celebrates Purim. One of those highly intelligent religious people who stew in their own contradictions for years, elaborating and tweaking, until their minds look like the inside of an M. C. Escher painting.
Most people like this will pretend that they are much too wise to talk to atheists, but she was willing to talk with me for a few hours.
As a result, I now understand at least one more thing about self-deception that I didn't explicitly understand before—namely, that you don't have to really deceive yourself so long as you believe you've deceived yourself. Call it "belief in self-deception".
When this woman was in high school, she thought she was an atheist. But she decided, at that time, that she should act as if she believed in God. And then—she told me earnestly—over time, she came to really believe in God.
So far as I can tell, she is completely wrong about that. Always throughout our conversation, she said, over and over, "I believe in God", never once, "There is a God." When I asked her why she was religious, she never once talked about the consequences of God existing, only about the consequences of believing in God. Never, "God will help me", always, "my belief in God helps me". When I put to her, "Someone who just wanted the truth and looked at our universe would not even invent God as a hypothesis," she agreed outright.
She hasn't actually deceived herself into believing that God exists or that the Jewish religion is true. Not even close, so far as I can tell.
On the other hand, I think she really does believe she has deceived herself.
So although she does not receive any benefit of believing in God—because she doesn't—she honestly believes she has deceived herself into believing in God, and so she honestly expects to receive the benefits that she associates with deceiving oneself into believing in God; and that, I suppose, ought to produce much the same placebo effect as actually believing in God.
And this may explain why she was motivated to earnestly defend the statement that she believed in God from my skeptical questioning, while never saying "Oh, and by the way, God actually does exist" or even seeming the slightest bit interested in the proposition.