Biblical scholars believe that the 12 apostles symbolically represent the 12 tribes of Israel, signifying the renewal of the covenant between God and humans. The 12 apostles were the original students and missionaries of Jesus' teachings and formed the beginnings of the new Christian church.
The 12 tribes of Israel were the original Jewish people mentioned in the Bible. When Jesus needed to pick students who would later spread his teachings, he is reported to have chosen a core group of 12 men to represent these tribes. This number helped reinforce his status as a Jewish prophet bringing new teachings to the world.
While many Christians believe in the 12 apostles as a factual and literal account, some Christians believe that Jesus actually had a much larger number of close students. They believe that the number 12 was added later by early Christians to reinforce the connection to Judaism. Others who believe in more than 12 students think that the number was symbolic and was meant to represent nations rather than individual people. In this belief, the individuals named as apostles may have existed and been chosen as representatives, or they may have been amalgams of many individuals.
In the Bible, the apostles' role was to study closely with Jesus when he went into seclusion. They were prepared for his death and resurrection in order to keep the faith alive. After his resurrection, they spread his teachings and laid the groundwork for the continuation of the Christian religion.