What caused the about face? Romans 3 starting with verse 10 gives a rather scathing description of the natural man. How does someone in that estate turn to God?
The Jews that were not intentionally "blinded" heard and chose to respond to the gospel message. Their actions was proof that faith came as a result of hearing the word of God; they believed what they were told. (Acts 2:37-41)
Consider that understanding predestination scriptures requires rightly dividing the word of truth. Paul makes reference to the fact that some Jews, were intentionally blinded in order that all of humanity would have the opportunity to be saved. See a portion of Paul's comments relative to this in Romans 11 below. Many Jews will remain blind until the time of the Gentiles is fulfilled.
Paul stated whosoever shall call upon the name of the Lord shall be saved. This applies to Gentiles, and Jews who were not intentionally "blinded."
Paul makes the point that obedience to the gospel is the result of faith produced by hearing the word of God:
"For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him.
13 For whosoever shall call upon the name of the Lord shall be saved.
14
How then shall they call on him in whom they have not believed? and how shall they believe in him of whom they have not heard? and how shall they hear without a preacher?
15 And how shall they preach, except they be sent? as it is written, How beautiful are the feet of them that preach the gospel of peace, and bring glad tidings of good things!
16
But they have not all obeyed the gospel. For Esaias saith, Lord, who hath believed our report?
17 So then faith cometh by hearing, and hearing by the word of God..." Rom 10:12-17
Note Paul's comments specific to the Jews:
Rom 11:7-11
What then? Israel hath not obtained that which he seeketh for; but
the election hath obtained it, and the rest were blinded
8 (According as it is written, God hath given them the spirit of slumber, eyes that they should not see, and ears that they should not hear unto this day.
9 And David saith, Let their table be made a snare, and a trap, and a stumbling block, and a recompence unto them:
10 Let their eyes be darkened, that they may not see, and bow down their back alway.
11 I say then,
Have they stumbled that they should fall? God forbid: but rather through their fall salvation is come unto the Gentiles, for to provoke them to jealousy.
12 Now if the fall of them be the riches of the world, and the diminishing of them the riches of the Gentiles; how much more their fulness?
13 For I speak to you Gentiles, inasmuch as I am the apostle of the Gentiles, I magnify mine office:
14 If by any means I may provoke to emulation them which are my flesh, and might save some of them.
15
For if the casting away of them be the reconciling of the world, what shall the receiving of them be, but life from the dead?"