God set up a covenant with the people he delivered from Egypt by Moses. This nation was Israel, the physical genetic descendants of Abraham, Isaac, and Jacob. A tabernacle was built by Moses in accordance with the pattern of the tabernacle that is in heaven. The true tabernacle. A priesthood was appointed, being the tribe of Levi. The descendants of Aaron, the brother of Moses, were to be the high priests of this tabernacle. Hebrews chapter 7 explains about the Aaronic priesthood and how it was unsatisfactory in making the people perfect. Another priesthood was then given by God to his people which did not descend from the lineage of Aaron but after the order of Melchizedek. The Melchizedek priesthood has no beginning of days and no end of days. This priesthood is eternal because of a life that does not end or die. This is the priesthood of Jesus. He is a high priest forever.
It is my understanding that some Hebrew Roots teaching of today says that we need to observe the appointed feasts of the tabernacle that Moses set up. These feasts are not necessarily the ones God established as recorded in the Bible, but are somehow related to Jewish tradition. The early church had something like this occurring in their midst. Jewish teachers previously practicing Judaism who were converted to Christ, were teaching that the church needed to observe the law of Moses and also to be circumcised.
Paul’s admonition in Galatians is that if the church did this they would be leaving the grace of God and putting themselves under the Law again. In which case they would be condemned by the law and would perish. They would have begun their walk with God in the Spirit and ended it in the flesh. God does not say in the Bible that he is going to add the Gentiles to the Jews. He states that he making a new man of the two that is neither Jew nor Greek.