Yes, Jesus’ earthly ministry was to Jews only, with the exception of one Gentile woman and one Gentile man who confessed their position under Israel.
And the “church” discussed in Matthew 16 describes the called out assembly of a believing Israeli nation, and that will take place in the future.
The “church” of Matthew 16 doesn’t describe anything we see on earth today that calls itself a church.
That was during His earthly ministry to the nation who should have received Him first.
Paul went to Jews first because Israel should have received Christ first. Then Israel would have been the evangelistic people to the remainder of the world.
The temple was supposed to be a house of prayer for ALL nations. It was unbelieving Israel that prevented this.
I don’t know if you quoted Geneis 18:17, 18 as a proof text that God doesn’t hide anything from anybody. That reference refers only to Abraham about the matter of Sodom. It doesn’t refer to every one of His servents in every situation in all times.
The disciples asked Christ (just prior to His Ascension) whether He would AT THAT TIME restore the kingdom TO ISRAEL. Our Lord told them that God was keeping that in His own power. Christ didn’t tell them whether it was now or later. The timing remained hid — a mystery.
I was thinking more along the lines of “all the nations of the earth shall be blessed in him”. That promise is to ALL nations, not just Israel.