The scriptures people call the New Testament or the Apostle's Writings are Jewish and Christian both. The early church, the church in its conception, was entirely Jewish.
Jeremiah 31:31-34 NASB - 31 "Behold, days are coming," declares the LORD, "when I will make a new covenant with the house of Israel and with the house of Judah, 32 not like the covenant which I made with their fathers in the day I took them by the hand to bring them out of the land of Egypt, My covenant which they broke, although I was a husband to them," declares the LORD. 33 "But this is the covenant which I will make with the house of Israel after those days," declares the LORD, "I will put My law within them and on their heart I will write it; and I will be their God, and they shall be My people. 34 "They will not teach again, each man his neighbor and each man his brother, saying, 'Know the LORD,' for they will all know Me, from the least of them to the greatest of them," declares the LORD, "for I will forgive their iniquity, and their sin I will remember no more."
Luke 22:20 NASB - 20 And in the same way He took the cup after they had eaten, saying, "This cup which is poured out for you is the new covenant in My blood.
Acts 5:31 NASB - 31 "He is the one whom God exalted to His right hand as a Prince and a Savior, to grant repentance to Israel, and forgiveness of sins.
Acts 11:18 NASB - 18 When they heard this, they quieted down and glorified God, saying, "Well then, God has granted to the Gentiles also the repentance that leads to life."