Paul stated that faith comes by hearing the Word of God. Next, he returned again to his leading question, "Isn't it God's fault that most of the Jews don't believe in Messiah?"
Romans 10:18-21 (KJV)
But I say, Have they not heard? Yes verily, their sound went into all the earth, and their words unto the ends of the world.
But I say, Did not Israel know? First Moses saith, I will provoke you to jealousy by them that are no people, and by a foolish nation I will anger you.
But Esaias is very bold, and saith, I was found of them that sought me not; I was made manifest unto them that asked not after me.
But to Israel he saith, All day long I have stretched forth my hands unto a disobedient and gainsaying people.
In verse 18 Paul asked, "Haven't the Jews heard the message about Messiah?" He answered a resounding, "Yes." He then quoted a part of Psalms 19.
Psalm 19:1-4 (KJV)
The heavens declare the glory of God; and the firmament sheweth his handywork.
Day unto day uttereth speech, and night unto night sheweth knowledge.
There is no speech nor language, where their voice is not heard.
Their line is gone out through all the earth, and their words to the end of the world. In them hath he set a tabernacle for the sun,
Paul focused on his earlier argument (Rom. 1:19-20) about creation and how it declared that there is a God. Just as he had said before, no one could claim ignorance about God. Considering that the Jews had the Torah, they especially could not claim ignorance.
Paul asked another leading question, "Didn't the Jews understand (verse 19)?" Although many didn't, Paul again left them no room for not understanding. He quoted Deuteronomy 32:21.
Deuteronomy 32:21 (KJV)
They have moved me to jealousy with that which is not God; they have provoked me to anger with their vanities: and I will move them to jealousy with those which are not a people; I will provoke them to anger with a foolish nation.
Because of the Word of God the Jews should have understood. Moses had even foretold what was going to happen. Because Israel had provoked God to jealousy, the Jews would also be provoked to jealousy by "them that are no people." God would also allow them to be angered by a "foolish" nation (probably a parallel phrase meaning the same group of people) because they had provoked Him to anger by the "work of their hands" (idolatry).
Deuteronomy 31:29 (KJV)
For I know that after my death ye will utterly corrupt yourselves, and turn aside from the way which I have commanded you; and evil will befall you in the latter days; because ye will do evil in the sight of the LORD, to provoke him to anger through the work of your hands.
In verses 20 and 21 Paul quoted Isaiah.
Isaiah 65:1,2 (KJV)
I am sought of them that asked not for me; I am found of them that sought me not: I said, Behold me, behold me, unto a nation that was not called by my name.
I have spread out my hands all the day unto a rebellious people, which walketh in a way that was not good, after their own thoughts;
The instrument of the Jews provocation would be the Gentiles. If the Gentiles were able to find Messiah, when they hadn't even sought for God, then the Jews had no excuse. Rather, God had continually stretched forth His hands to the Jews who were a disobedient and gainsaying (contradictory) (obstinate) people.
The story of the Jews doesn't end here. Chapter 11 will continue to address their issue. Perhaps a clue can be found at the end of the Deuteronomy passage.
Deuteronomy 32:43 (KJV)
Rejoice, O ye nations, with his people: for he will avenge the blood of his servants, and will render vengeance to his adversaries, and will be merciful unto his land, and to his people.