The whole Bible is for us (Gentiles) however, it's not all about us or pertaining to us. Matthew through John, for instance, is written to the Lost sheep of the House of Israel. Matthew 15:24 Jesus states: "But he answered and said, I am not sent but unto the lost sheep of the house of Israel." He didn't include us Gentiles in that statement of fact.
You are proof-texting. that actually happened during an encounter with a non-Jew who 'had more faith that all of you in Israel.'
This has been treated many times. He got about 220 missionaries ready by the time he finished the seminar between the resurrection and Pentecost (Lk 24). They practiced in Israel, and were all set for 'the ends of the earth' Mt 28:19, Mk 13:15, etc. Indeed, the plan was to make as many people in Israel missionaries to 'the islands and distant shores' as possible, because they had the background in the Scriptures.
The Bible is not chopped up between programs and full of 'switch-over' moments etc as D'ism has been declaring for 150 years, as though we 'needed' it to make sense of the Bible. Someone 'voided and replaced' the promise to all nations, says Gal 3:17, and that still needs to be cleared up and sorted.