It comes by hearing...i.e...an outside source. Faith is not innate, nor does it resonate from man.(said by SovereignGrace)
For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek. (Rom 1:16)
And this is how faith cometh by hearing, and hearing by the Word of God.