(Acts 28:23-28) Isa 6:9-10, Acts 13:46-48, Acts 18:6

In the Old Testament, it was prophesied that the people of Israel would not understand the gospel of God. (Isa 6:9-10)

Isa 6:9 And he said, Go, and tell this people, Hear ye indeed, but understand not; and see ye indeed, but perceive not. 10 Make the heart of this people fat, and make their ears heavy, and shut their eyes; lest they see with their eyes, and hear with their ears, and understand with their heart, and convert, and be healed.

In the end, as prophesied in the Old Testament, the Jews did not understand the gospel that Jesus was the Christ. So, the gospel of God's salvation was directed to the Gentiles. (Acts 28:23-28, Acts 13:46-48, Acts 18:6)

Acts 28:23 And when they had appointed him a day, there came many to him into his lodging; to whom he expounded and testified the kingdom of God, persuading them concerning Jesus, both out of the law of Moses, and out of the prophets, from morning till evening. 24 And some believed the things which were spoken, and some believed not. 25 And when they agreed not among themselves, they departed, after that Paul had spoken one word, Well spake the Holy Ghost by Esaias the prophet unto our fathers, 26 Saying, Go unto this people, and say, Hearing ye shall hear, and shall not understand; and seeing ye shall see, and not perceive: 27 For the heart of this people is waxed gross, and their ears are dull of hearing, and their eyes have they closed; lest they should see with their eyes, and hear with their ears, and understand with their heart, and should be converted, and I should heal them. 28 Be it known therefore unto you, that the salvation of God is sent unto the Gentiles, and that they will hear it.

Acts 13:46 Then Paul and Barnabas waxed bold, and said, It was necessary that the word of God should first have been spoken to you: but seeing ye put it from you, and judge yourselves unworthy of everlasting life, lo, we turn to the Gentiles. 47 For so hath the Lord commanded us, saying, I have set thee to be a light of the Gentiles, that thou shouldest be for salvation unto the ends of the earth. 48 And when the Gentiles heard this, they were glad, and glorified the word of the Lord: and as many as were ordained to eternal life believed.

Acts 18:6 And when they opposed themselves, and blasphemed, he shook his raiment, and said unto them, Your blood be upon your own heads; I am clean; from henceforth I will go unto the Gentiles.