Martin Scorsese says, "Faith and doubt cannot be separated..."
He is wrong.

Faith...

Those who do not know the Spirit accuse the prophets who wrote the Bible of blindly but creatively theorizing about the existence of some higher imperceivable power... and dismiss it as antiquated superstition. Any reference to prophecy is easily explained away as coincidence, or a product of textual forgery and manipulation over the centuries. Ultimately, the spiritless demand proof.

Those who do know the Spirit immediately recognize the true author of the Scriptures by their commonality of content, and ceaseless reference to symptoms of spiritual intervention that only the Spirit filled appreciate and understand. Holy Scripture is a joyful validation for the spiritually attuned and is easily accepted as fact. The sheep recognize the call of their shepherd.

So, how does "one who knows" describe the indescribable? How do the spiritually enlightened explain the unseen? The one who knows is content and does not toil with mystery, but is a mystery for those who do not know. What word describes the difference between the two?

No, it is not faith.

The knowledgeable man knows that he knows and does not require faith. Faith then becomes an accusation of the ignorant; Faith is belief in the unreasonable and unfounded they say... The man of Spirit already knows his purpose and place in life. The man of logic and reason requires faith to sleep at night.

New King James Version
Hebrews 11
""1)Now faith is the substance of things hoped for, the evidence of things not seen. 2)For by it the elders obtained a good testimony.
3)By faith we understand that the worlds were framed by the word of God, so that the things which are seen were not made of things which are visible.""

So, what is faith for the one who doubts?
It is undeniable proof of creation and God's gift of Spirit as evidenced by the faithful.
It is an unyielding desire for a spiritual confirmation of truth despite the authors of fairy tales... or, despite better judgment.

NIV
Ephesians 2; 8-10
""8)For it is by grace you have been saved, through faith—and this is not from yourselves, it is the gift of God— 9)not by works, so that no one can boast. 10)For we are God’s handiwork, created in Christ Jesus to do good works, which God prepared in advance for us to do.""

JAPOV
Believers are saved by God's grace through faith, which is an unearned and undeserved gift of Spirit. No man can stand justified before God and boast of his own righteousness by his own hand. We are God's own will and work of Spirit, created in Christ Jesus to do God's will... Which was His plan from the foundation of the earth.