RWP is instructive; 1Co 5:8 - Wherefore let us keep the feast (hōste heortazōmen). Present active subjunctive (volitive). Let us keep on keeping the feast, a perpetual feast (Lightfoot), and keep the leaven out. It is quite possible that Paul was writing about the time of the Jewish passover, since it was before pentecost (1Co_16:8). But, if so, that is merely incidental, and his language here is not a plea for the observance of Easter by Christians. The Greeks could not keep any perpetual feast, they were never given the feasts. The feasts belong to Israel. The OT makes this abundantly clear.And this is always true, being that it is unreasonable to build doctrine from one verse.There are just way too many verses showing what manner of behavior and ideas it was that caused the riotous behavior of the Jews, namely that a gentile had been allowed in the synagogue, to say nothing of a transference of Israel's carnal things.re:Acts 16 1Then came he to Derbe and Lystra: and, behold, a certain disciple was there, named Timotheus, the son of a certain woman, which was a Jewess, and believed; but his father was a Greek:Yes, but his MOTHER was a Jewess, i.e. not a gentile.re:Acts 13:5 (King James Version)King James Version (KJV)And when they were at Salamis, they preached the word of God in the synagogues of the Jews: and they had also John to their minister.I don't know how that verses supports non Jews being in the synagogues or at the feasts, indeed, Paul did not preach to gentiles until he exited the synagogue to those who were already believers and already standing outside the middle wall of partition. The Bible is quite clear about these things. Paul first preached to Jews only for nine years, then he preached to both Jew and Greek, but it was always to the Jew first. Afterwards he would go outside the middle wall of partition and share that message which belonged to the Jews with the Greeks. But it was Israel's message.Regarding the other verses you post, there were no gentiles involved in the synagogue. At no time was the gentile treated as equal during the Acts. Surely when we make the Scriptures say they were anything close to going beyond prophetic fulfillment is becomes a Scriptural problem. The feasts and the oracles of God, the covenant relation with God, all of it belongs to Israel. I would think that the OT makes this quite clear. While the NT brings the possibility of fulfillment, none of Israel's things are prophecied to be shared with all the nations. That is what sets Israel apart, their close association with Christ as mediators to be that chosen channel of blessing to the nations.It is for this cause that it is written ~Rom 15:27 It hath pleased them verily; and their debtors they are. For if the Gentiles have been made partakers of their spiritual things, their duty is also to minister unto them in carnal things. Writing specifically to the Jews, Paul is inspired to write ~1Co 9:11 If we have sown unto you spiritual things, is it a great thing if we shall reap your carnal things?While gentiles were being used by GOD to provoke Israel, as per prophecy, they were permitted to metaphorically sit at Israel's table, but it was still Israel's table. Why, when the hope of Israel was in view, it was awfully difficult for a non Jew to get anything from the Jew. Christ is our example in this, for HE told the Syrophenician woman HE was not SENT but to Israel. But first, "HE answered her not a word".