Of themselves no one can believe because the unsaved are spiritually blind. How could it be any clearer
and direct than this:
[Jhn 12:37-40 KJV]
37 But though he had done so many miracles before them, yet they believed not on him:
38 That the saying of Esaias the prophet might be fulfilled, which he spake, Lord, who hath believed our report? and to whom hath the arm of the Lord been revealed?
39 Therefore they could not believe, because that Esaias said again,
40 He hath blinded their eyes, and hardened their heart; that they should not see with [their] eyes, nor understand with [their] heart, and be converted, and I should heal them.
[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.
[1Co 2:13-14 KJV]
13 Which things also we speak, not in the words which man's wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual.
14 But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know [them], because they are spiritually discerned.