This is why I have such a problem in continuing to follow the OT. It does nothing for the Gospel message. I just don't see how a person can be Christian and Jew. The Jews had to become Christian or remain Jews (Judaism).
Jesus did not come to start his own religion, but was born a Jew, raised a Jew, became a Jewish rabbi, had Jewish disciples, is the Jewish Messiah, fulfilled Jewish prophecy, will return as the Lion of Judah, and came to bring fullness to Judaism. At its origin, Christianity was a sect of Judaism. For roughly the first 7-15 years after Messiah's resurrection up until in inclusion of Gentiles in Acts 10, all Christians were Torah observant Jews. There is absolutely nothing that says that Jews need to stop being Jews in order to become Christians, and in fact they faced the opposite issue in Acts 15, where they were discussing whether Gentiles had to become Jews in order to be Christians. It is just as false that Gentiles need to become Jews in order to be Christians as it is that Jews need to become Gentiles in order to become Christians.
Abraham knew the day was coming. It was a time of angels. Like Mary, he was told of an event to occur. by angels. Abraham lived by faith only. Truth had not come (yet). And, once again, Jesus tells the Jews that they were not following (the true) God, the Father.
John:
53 Art thou greater than our father Abraham, which is dead? and the prophets are dead: whom makest thou thyself?
54 Jesus answered, If I honour myself, my honour is nothing: it is my Father that honoureth me; of whom ye say, that he is your God:
55 Yet ye have not known him; but I know him: and if I should say, I know him not, I shall be a liar like unto you: but I know him, and keep his saying.
56 Your father Abraham rejoiced to see my day: and he saw it, and was glad.
So when I read that Abraham saw and talked to God, that Moses heard God and the Lord said, then I hear Jesus say:
John:
37 And the Father himself, which hath sent me, hath borne witness of me. Ye have neither heard his voice at any time, nor seen his shape.
38 And ye have not his word abiding in you: for whom he hath sent, him ye believe not.
Yes, Abraham was a good man seeking truth. But it didn't exist. He knew it was coming. He was saved by his faith and Jesus surely knew him at the resurrection (when he resurrected the dead).
The truth has come. It is here. Why would I desire to find it in the OT? I see the Jews waiting. I don't have to wait.
In Matthew 15:2-3, Jesus was asked why his disciples broke the traditions of the elders and he responded by asking them why they broke the command of God for the sake of their tradition. He went on to say that for the sake of their tradition they made void the Word of God (Matthew 15:6), that they worshiped God in vain because they taught as doctrines the commands of men (Matthew 15:8-9), and that they were hypocrites for setting aside the commands of God in order to establish their own traditions (Mark 7:6-9), so what the Pharisees were teaching as the Mosaic Law was actually their own traditions, and this was a major source of conflict between them and Jesus. It is critically important to make this distinction in order to correctly understand what is being said about the laws of men and what is being said about the laws of God because Jesus never spoke against the Judaism that was instructed by God, only against what the Pharisees were teaching.
According to John 5:46, Jesus said that Moses wrote about him, according to Luke 24:27, Jesus began with Moses and the Prophets interpreting to them all the things in Scriptures concerning himself, according to Hebrews 10:7, the totality of the scroll is written about Jesus, and according to Romans 10:4, a relationship with Jesus is the goal of the Law for all who have faith. The Law is all about Messiah and about how to have a relationship with Him based on faith and love, but the Law can be outwardly obeyed without being inwardly focused on growing in a relationship with God, which is completely missing the whole point of obeying the Law, and why Israel failed to obtain righteousness (Romans 9:30-32), and why Paul considered that to be rubbish (Philippians 3:8).
Everything that is taught in the NT is dependant on what was taught in the OT. In Acts 17:11, the Bereans were praised because they diligently tested everything that Paul said against OT Scripture to see if what he said was true. The NT authors quoted or alluded to the OT thousands of times in order to establish that it supported everything they said and to show that they did not depart from it. The Law is the way (Deuteronomy 8:6, Jeremiah 6:16-19, Psalms 119:1), the truth (Psalms 119:142), and the life (Deuteronomy 30:15-20, Proverbs 3:18, Matthew 19:17), Messiah is the way, the truth, and the life (John 14:6), the Law is God's Word, and Messiah is God's word made flesh, so there is no separating following one from following the other. Jews teaching obedience to the Torah, but they don't teach to follow the Messiah, Gentile believers teach to follow the Messiah, but don't teach obedience to God's Torah, so both have the truth, but both only understand half of it.