When Jesus began His ministry here on earth, He chose 12 men to be His first disciples. A disciple is similar to a student and the Master Rabbi began to teach them. Later the disciples were sent out into the world to represent His teachings. Through their faith and education the disciples became apostles (representatives, messengers, emissaries). Although similar in nature they is a difference between a disciple and an apostle. A person needs to be a disciple (trained by the teacher) before they can be an apostle (representative of the teacher).
Other people besides the 12 men were also referred to as apostles showing that the Messiah's followers were growing in size and understanding of God's revelations. There were thousands of Jews who had put their faith in Messiah Jesus. 3,000 in a single day during the holiday of Shavuot (Pentecost), the day the Holy Spirit came (See Acts 2).
As time went on some of the Jewish believers who recognized Jesus as their Messiah were being referred to as "The Way" (Acts 9:2). Probably based on Jesus teaching that, “I am the way, and the truth, and the life; no one comes to the Father but through Me (John 14:6)." Saul (whose Greek name was Paul) was en route to arrest members of this Jewish group "The Way" before his encounter with the Christ on the Road to Damascus. Once Saul, who was a well respected Pharisee and a student himself at the school of Hillel realized that Jesus was the Messiah, the group of Jewish believers continued to grow and thousands of Jews and some Gentiles were now belonging to this sect. Believing in Jesus as the Messiah put the group at odds with the San Hedrin Court who refused to recognize the Kingship and Messiahship of Jesus, and who had given Saul/Paul the authority to be on his way to Damascus in the first place.
As time went on the separation inside Judaism continued to occur. Many New Testament authors still worshiped and taught at the temple in Jerusalem until its destruction by Rome in A.D.70. There were more than 500 people who saw the resurrected Christ during the 40 days He walked through Israel before ascending into heaven. The New Testament authors were allowed to tell about Him because there were so many witnesses who saw Jesus. As time went on, the witnesses grew older and became harder to find and the Apostles began to be punished for telling the testimony of the risen Saviour. Saul wrote some of his letters from prison, signing them using his Greek name Paul.
After Rome destroyed the Second Temple Judaism was at a crossroads. To some it was obvious that God had made the way for a permanent blood sacrifice to be in place through the Messiah just as Isaiah 53 teaches it will happen. Those people believed God had brought this to be before He allowed or caused the Temple to be destroyed.
For Jews who didn't believe that, there was no longer a way to fulfill the commandments of bringing sacrifices and First Fruits to the temple as offerings.
If Judaism was to continue there would need to be some changes. Judaism began to change over from the biblical Judaism that included daily sacrifices to finding other ways to receive God's atonement. Judaism was transformed from Biblical Judaism (atonement being made by substitutional blood animal sacrifices - See Lev. 17:11) into Rabbinical Judaism (atonement through charity, good deeds and works).
Around 135 A.D. the leading Rabbi (Rabbi Akiva) believed that a man named Simon ben Kosiba (more commonly known as Simon bar Kochba) was really the Messiah. Rabbi Akiva believed Bar Kochba was going to lead Israel out of Rome’s military control through an uprising, and convinced thousands of Jews to follow him into battle. History has proved that, Bar Kochba was no messiah and sadly thousands of Jews died, following this guidance.(1)
When it came time for battle the Jews who recognized Jesus as their Messiah would not fight for and under Bar Kochba because they knew he wasn't really the Messiah even though Rabbi Akiva and others claimed that he was. Because they refused to recognize Bar Kochba as the Messiah and refused to do battle with Rome because Bar Kochba was the leader of Israels army, the separation between Jewish believers in Jesus and the rest of Israel took its biggest step and Jews that were part of "The Way" were no longer though of as being part of Israel. They were now considered a religion with a separate identity, known as Christianity.
From 135 A.D. to 323 A.D. Those who recognized Jesus as their Messiah worshiped in a combination of Jewish tradition and Gentile tradition. In 323 A.D. when Constantine became Emperor of Rome he outlawed Jewish customs and traditions for Christians including Saturday Sabbath worship. Christianity and Judaism seemed like two separate religions even though Jesus was Jewish. In the absence of Jewish customs, culture and traditions Christianity began to include some Pagan acts of worship like celebration on December 25. Before it was decided that Jesus birthday would be celebrated on that day Dec. 25 was already a pagan holiday. Sunday was already a pagan day of worship to honor the Sun God. There are other religious practices that even though today they are meant to bring honor to Jesus, there origination was pagan.
Jewish tradition was now removed from Christianity even though the original intent was for Judaism to realize that the Mosaic Covenant was ending and the prophesied New Covenant was to begin. This New Covenant has began for Jews on an individual basis and when Messiah comes back, Israel as a nation will embrace it as well. At that time Israel will look on Him that they pierced, crying out - Blessed is He who comes in the Name of the Lord.
Today, Messianic Judaism (which is growing at unparalleled numbers) is defined as people who recognize Yeshuah, (Jesus Hebrew name) as Lord and Saviour. They have chosen to celebrate and observe some things in the Old Testament not in place of Christ but to honor Him. One practice that both Christians and Messianic Jews do to honor the Lord is to take communion in remembrance of Him. When biblical Feast Days are observed, one can find the Messiah has fulfilled these days full of meaning and a great appreciation of what Messiah has done for us can be found.
Embracing some of the culture, customs and traditions of our Messiah is not wrong, especially since it can lead us to have a greater attitude of gratitude. God made every believer in Jesus different in one way or another. The goal is to not all be the same but to celebrate our diversity as one body.
1). A Rabbi Looks At The Last Days by Rabbi Jonathan Bernis p.82