All of this is found in the OP. The GC you've cited was given to Jews, for Jews Only. Acts 11:19 below speaks directly to your question.
Matt 15:24 Messiah answered & said, I am not sent but unto the lost sheep of the house of Israel.
(SCRIPTURE PROCLAIMS: Jesus was sent, ONLY, to the lost sheep of the ""House of Israel"")
Rom 15:8 I say that Messiah was a minister of the circumcision for the truth of God, to confirm the promises made unto the fathers:
(SCRIPTURE PROCLAIMS: Messiah was sent to minister to the circumcision/JEWS, To fulfil OT promises made to the Hebrew fathers)
Acts 11:19 Now they which were scattered abroad upon the persecution that arose about Stephen travelled as far as Phenice, and Cyprus, and Antioch, preaching the word to none but unto the Jews only.
(MY NOTE: This is after Stephens death (6 yrs after Jesus death & resurrection) these Jewish converts that had fled Israel. Running for their lives from law zealots like Saul. They are still only sharing Christ with OTHER JEWS!).
Acts 10:28 Peter said unto them, Ye know how that it is an """unlawful""" thing for a man that is a Jew to keep company, or come unto one of another nation; but God hath shewed me that I should not call any man common or unclean
(BTW: Jesus died on the cross 7 yrs before Peter tells Cornelius (an Italian/gentile) "IT'S UNLAWFUL" for a Jew to hang out with a gentile, Jesus faithfully kept the law)
Matt 15:26 Jesus said; It is not meet to take the children's bread, and to cast it to dogs.
(MY NOTE Jesus calls this gentile woman of Canaan (that He helped) a dog. Jews often referred to Gentiles as "dogs" Matt 7:6)
Gentiles were considered (like dogs) unclean/ungodly (living outside of covenant seals & purification laws). Just being in their presence could make a Jew ceremonially unclean (Jn 18:28)
Gal 4:
4 But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law,
5 To redeem them that were under the law, that we might receive the adoption of sons.
(SCRIPTURE PROCLAIMS: God sent forth his Son """made under the law""" to """redeem those under the law/JEWS""")
Jesus's in the flesh mission was to the lost sheep of the ""House of Israel"" ONLY!
A/the new covenant (that will include gantiles) doesn't/can't begin until after Jesus dies.
Heb 9:
16 For where a testament is, there must also of necessity be the death of the testator.
17 For a testament is of force after men are dead: otherwise it is of no strength at all while the testator liveth.
(MY NOTE: Jesus kept, lived, taught & fulfilled the old covenant Mosaic laws. There can be no new covenant until after Jesus (the Testator) dies.
Study tips from a pro:
Myles Coverdale; Bible theologian/translator. He wrote the Coverdale Bible. Say's don't judge scripture by what is spoken, or written only.
When dissecting any verse of scripture. Ask yourself, of whom, to whom, with what words, what time, where, to what intent, with what circumstances, considering what is written before and what follows any single verse context.
Who was preaching? JESUS, John & the 12!
Who was Jesus preaching to? JEWS UNDER THE LAW! Reread Matt 15:24, Rom 15:8 above.
What's the timeframe? PRE-DEATH!
Where? ISRAEL!
To what intent? REDEEM THOSE UNDER THE LAW/JEWS! Reread Gal 4:4-5 above.
Jesus earthly mission was to/for Israel ONLY! This message is void of Jesus sin atoning death & resurrection. The OT God given Levitical animal sacrificial system dealt with (covered) Israel's sin.
Gentiles had NO PART in the All Jewish gospel of the kingdom message.
A glimpse of God's promised coming Kingdom to Israel:
2 Sam 7:12-13, 1 Chron 17:10-14, Isa 9:6-7,11:1-9, Dan 2:44,7:13-14, Mic 4:1-5, Zec 14:1-21, Lk 1:32-33.