Read Hebrews 8.
Christianity is rooted in Judaism. Most of our scriptures are Hebrew documents written for Jewish people living in Israel. Our Lord Jesus was the Messiah who was prophesied about in those Hebrew scriptures. His death on the cross was the final, perfect sacrifice foreshadowed by the uncountable number of animals who were offered on the altar of the tabernacle and the temple.
Given all of this, why are we Christians not more Jewish in our practice of Christianity? The answer is here in Hebrews 8. And, that answer, too, is rooted in the Hebrew scriptures. In Jeremiah 31:31-34, quoted here in Hebrews 8:8-12, God promised to make “a new covenant with the people of Israel and Judah” (v. 8). Verses 9-12 describe this covenant and, among other things, they tell us, “No longer will they teach their neighbor, or say to one another, ‘Know the Lord,’ because they will all know me, from the least of them to the greatest. For I will forgive their wickedness and will remember their sins no more.” This promise has begun to be fulfilled in Jesus. He mentioned this when he turned the elements of the Passover feast into the Lord’s Supper and said, “this cup is the new covenant in my blood” (Matt 26:28, Lu 22:20, 1 Cor 11:25). The fact that we Gentiles would be part of this new covenant is indicated here in Hebrews 8:11, “No longer will they teach their neighbor… ‘Know the Lord….’” We Gentiles are “their neighbor.”
The reason, then, that we don’t practice Jewish feasts and festivals and keep the Law of Moses is that, according to verse 13, “By calling this covenant ‘new,’ he has made the first one obsolete; and what is obsolete and outdated will soon disappear.” These Old Testament ceremonies, symbols, and laws are unnecessary anyway because, as verse 10 put it, “I will put my laws in their minds and write them on their hearts.” We have a new nature and the Holy Spirit dwelling within us! There are still blessings promised in the new covenant that await us, but we have God’s power within us to wait for them, to grow in our knowledge and love of him while we wait, and to call others to “know the Lord.”