The Torah.
Many Christians make the mistake of thinking the Torah , the Old Testament, are irrelevant today. They admonish we are to be in the New Covenant, not the old. But that's a mistake. Often this idea arrives because one is speaking with someone who is a follower of what is called, Supersessionism or, "Replacement Theology". They assert that the chosen of God are no longer the Jews, but those who are Christian. Forgetting that the first "Christians" were mostly Jews. It is a form of Antisemitism in arguing that the New Covenant through the blood sacrifice of Jesus supersedes the Old Covenant and because that was a covenant made exclusively for the Jewish people.
Our church was founded on the day of Pentecost. Which according to the Jewish calendar is the holy day of Shauv’ot.
You might find this useful.Torah Awareness -Why Christians Should Study Torah
https://hebrew4christians.com/Articles/Torah-Aware/torah-aware.html
"...The "Church" was born on a Jewish holiday of Shauv’ot (Pentecost) among the Jewish people in Jerusalem. Peter's sermon during that festival (Acts 2:1-41) was entirely Jewish, copiously quoting from the prophets and David, which would have meant little to any Gentiles in earshot (if there were any). It is likely, therefore, that the 3,000 people who were saved that day would have been all Jewish. The earliest members of the new church met regularly in the Temple, where Gentiles were explicitly excluded (Acts 2:46). Note that the apostles Peter and John are recorded to have gone to the Temple for prayer during the time of the minchah (afternoon) sacrifices (Acts 3:1), and their ministry continued exclusively among the Jewish people, "among whom were thousands who believed and were zealous for the Torah" (Acts 21:20). Even after they were imprisoned but miraculously escaped, an angel told them to "Go, stand and speak in the Temple to the people all the words of this life" (Acts 5:20). "