Romans 10:19 But I say, did Israel not know? First Moses says: "I will provoke you to jealousy by those who are not a nation, I will move you to anger by a foolish nation." 20 But Isaiah is very bold and says: "I was found by those who did not seek Me; I was made manifest to those who did not ask for Me." 21 But to Israel he says: "All day long I have stretched out My hands To a disobedient and contrary people." (NKJ)
If we follow Paul's line of argument we see that he is contrasting two groups of people, the Jews and those who are not Jews (gentiles), and he is saying that the Jews (speaking in generalities) have not found the Savior while the gentiles have.
The point being made is that those who were looking for the messiah did not receive him; however, those who did not have the Old Testament promises did.
Here is what some commentators have written on the verse:
The Gentiles, their minds and hearts-darkened by sin, and therefore
not even asking for God’s help, receive it. Israel is passed by
because of its obstinacy, as is clear from verse 21. But concerning
Israel he says,“All day long I have stretched out my hands to a
disobedient and obstinate people.” [Hendriksen, W., & Kistemaker, S.
J. (1953–2001). Exposition of Paul’s Epistle to the Romans (Vol.
12–13, p. 353). Grand Rapids: Baker Book House.]
Paul’s point in vs 18–20 is to show that Israel has, indeed, both
‘heard’ the word of Christ and ‘known’ about God’s plan of salvation
as it has now been unfolded through the preaching of the gospel. Paul
probably quotes Ps. 19:4 (v 18b) not as a prophecy of the preaching of
the gospel, but simply in order to use its language to assert the
widespread proclamation of the gospel to Jews throughout the
Mediterranean world. It is perhaps the reference to ‘the ends of the
earth’ in this quotation that leads Paul in vs 19–20 to reflect on
what was for the Jews of his day a key ‘stumbling block’ in the way of
accepting the gospel: the inclusion of Gentiles in the church. Paul
shows from both Moses (Dt. 32:21) and Isaiah (65:1) that God had
planned all along to include the Gentiles in his ultimate plan of
salvation and to make them his people (cf. 9:24–26). Continuing his
quotation from Isaiah (65:2), Paul concludes this section of his
argument by reminding his readers of two key facts: God has constantly
been extending the word of his grace, the gospel, to the Jews; but
they, for their part, have been largely disobedient and
obstinate. [Carson, D. A., France, R. T., Motyer, J. A., & Wenham, G.
J. (Eds.). (1994). New Bible commentary: 21st century edition (4th
ed., p. 1147). Leicester, England; Downers Grove, IL: Inter-Varsity