Your lack of understanding is only outweighed by your refusal to believe what is written.
I would never refuse to believe what is written. I have no problem refusing to believe what you think is written, though.
Don't be ignorant of this mystery.
Romans 11
25 For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in.
What that mean?
Read the rest of Romans 11 from the beginning and you can see what it means. Do you know what it means for "blindness in part" to have "happened to Israel"?
Romans 11:1 I say then,
has God cast away His people? Certainly not! For I also am an Israelite, of the seed of Abraham, of the tribe of Benjamin. 2 God has not cast away His people whom He foreknew. Or do you not know what the Scripture says of Elijah, how he pleads with God against Israel, saying, 3 “Lord, they have killed Your prophets and torn down Your altars, and I alone am left, and they seek my life”? 4 But what does the divine response say to him? “I have reserved for Myself seven thousand men who have not bowed the knee to Baal.” 5
Even so then, at this present time there is a remnant according to the election of grace. 6 And if by grace, then
it is no longer of works; otherwise grace is no longer grace. But if
it is of works, it is no longer grace; otherwise work is no longer work. 7
What then? Israel has not obtained what it seeks; but the elect have obtained it, and the rest were blinded.
Blindness in part happened to Israel in the sense that there was an elect remnant of believers that obtained what it sought (salvation by grace through faith in Christ) "and the rest were blinded" and cut off because of their unbelief (Romans 11:20). So, part of Israel was saved in Paul's time and part was blinded. So, what Paul was saying in Romans 11:25 is that would continue until the fullness of the Gentiles comes in. And the reason for that is because the process that started back then is God's plan for saving Jews and Gentiles. His plan was first for the Jews to preach the gospel and bring salvation to the Gentiles and then He turned it around to have Gentiles bring the gospel and salvation to the Jews. Here is how Paul explained that plan...
Romans 11:11 I say then,
have they stumbled that they should fall? Certainly not! But through their fall, to provoke them to jealousy, salvation has come to the Gentiles. 12 Now if their fall
is riches for the world, and their failure riches for the Gentiles, how much more their fullness! 13 For I speak to you Gentiles;
inasmuch as I am an apostle to the Gentiles, I magnify my ministry, 14 if by any means I may provoke to jealousy those who are my flesh and save some of them.
As Paul explained here, the Israelite who were blinded stumbled, but they did not fall. God's plan was to bring salvation to the Gentiles who, in turn, would provoke the blinded Israelites to jealous and make them want to be saved as well. And we know that Paul himself believed he would lead some of those blinded Israelites to salvation because he said in relation to his fellow Israelites who had been blinded: "inasmuch as I am an apostle to the Gentiles, I magnify my ministry, if by any means I may provoke to jealousy
those who are my flesh and save some of them.". So, this process started way back then and I'm sure there were a good number of Israelites whose blindness was removed when they were led to salvation by Paul and others. And that has been happening ever since and will continue until the fullness of the Gentiles comes in.
