The gentiles had no covenant with God in those generations back in the Old Testament and there was no body of Christ either.
Jerry, when Israel came out of Egypt, non-Israelites came with them. Depending on your translation, they are called strangers or foreigners... but the Hebrew is clear, they were not Israelites. When they all got to Mt. Sinai, we see three things said by God concerning those non-Israelites...
1. They were to assimilate into the tribes they traveled with.
2. The law was given to Israel AND the non-Israelite with them
3. Israel was to treat THEM as if "native born."
Your idea, the mainstream Christian idea, that gentiles were not part of the covenant at Sinai is wrong, sorry, there is no other way to say it. From the very beginning, it was Israel >>AND<< those non-Israelites that chose to walk with them, follow their God, and live by their ways.
Zechariah shows the feasts will be located the land of Israel where David will be king over the Jews not the body of Christ as the spiritual Jew theory implies.
Of course the Feasts will once again happen in the land of Israel. However, it will not be "David" but rather Yeshua, Jesus... who will reign. Are you familiar with the two messiah theology of the Jews? Long ago, before Yeshua walked the earth, certain teachers would teach that there would be two Messiah's...
1. Mashiach ben Yosef (Messiah son of Joseph) the suffering servant
2. Machiach ben David (Messiah son of David) the Conquering King
Zechariah is simply speaking about King Messiah, not suffering servant Messiah. WE KNOW that this is the same guy... He came as the suffering servant, He returns as the Conquering King... but same guy. So when Zechariah uses "David" there.... it is speaking of the King Messiah. He will not be the King over the Jews Jerry, He will be the King over the ENTIRE House of Israel which includes the Jews... and you, and me, and all the other Christians. By the way, Zech 12:10 reveals how the "Jews" will come to see Him for who He is. And yes, that verse is speaking about only Jews. The inhabitants of the city of David is Jews (primarily).