Now, just in case I completely missed the point of your question in my first reply, let me try again, assuming that your question has to do with how a person can go from UNBELIEF (atheism, for example) to suddenly believing the Gospel.

That's the same kind of question that Nicodemus asked the Lord (John's gospel, chapter 3):

"How can a man be born again? Can he enter the womb a second time and be born?"

Jesus, of course, was talking about spiritual rebirth rather than physical. And in fact, it is as you describe it - supernatural.

Faith is not possible for one who has not been "born again!" But the New Birth is from Above, not from within. It takes place when God sovereignly and supernaturally gives new life to a soul that had been dead. A captive will must first be freed from it's bondage before it is free to accept the truth of the Gospel.

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But a natural [unregenerate, not yet born again] man does not accept the things of the Spirit of God, for they are foolishness to him, and he cannot understand them, because they are spiritually appraised (1st Corinthians 2:14, NASB).

It really does take a miracle to believe the gospel.