If someone believes that their faith has saved them, then their salvation is by their action and not Jesus's
which violates the Gospel and therefore is impossible
Not only does our faith "not really save us" - it cannot save at all.
The true believe comes from being born-again - a fruit of the Spirit.
Becoming born-again happens to only those who are saved, not before.
Until that happens no one is able to hear or believe because the god of this world - satan-
has blinded all of the unsaved.
[
2Co 4:4 KJV] 4 In whom the
god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.