The Greek word “apostolos” means ambassador, delegate, or messenger. It stems from a base word “apostellō” meaning “sent out” or “sent away”. In Biblical use, it means someone sent out on a mission. That mission is sharing the Gospel, the good news that Jesus has provided a way to be reconciled with God ¹.

The First Apostles

Now the names of the twelve apostles are these: The first, Simon, who is called Peter, and Andrew his brother; and James the son of Zebedee, and John his brother; Philip and Bartholomew; Thomas and Matthew the tax collector; James the son of Alphaeus, and Thaddaeus; Simon the Zealot, and Judas Iscariot, the one who betrayed Him.

Matthew 10:2-4

And He called the twelve together, and gave them power and authority over all the demons and to heal diseases. And He sent them out to proclaim the kingdom of God and to perform healing…
When the apostles returned, they gave an account to Him of all that they had done.

Luke 9:1-2, 10

As the book of Acts describes the activities of the early church, one of the first was to choose a new twelfth apostle to replace Judas the betrayer. The replacement had to be someone who had been with Jesus from the beginning, along with the other eleven disciples, someone who could give firsthand eyewitness testimony the same way that they could. Acts 1:21-26 describes the process used to choose Matthias.

Throughout Acts, the apostles are shown to be preaching with great power, including miraculous healings. All of the new believers — thousands of them — were hanging on their every word, eager to hear everything they could teach about Jesus and His salvation. The apostles were the leaders and decision-makers among the church, as well. When the church grew beyond what the apostles could handle in person, they called for another group of trustworthy men, the deacons, to take over the more mundane tasks. That left the apostles free to continue their main task of sharing the Gospel.

The Apostle Paul

The last man chosen by Jesus to be an apostle was a special case. Originally, Saul was anything but a disciple of Jesus. He was a Pharisee, educated under Gamaliel (a very well-respected teacher of Jewish law). As the first deacon, Stephen, was being stoned to death for preaching the gospel, Saul was standing by, approving of the execution and holding the coats for the executioners! (Acts 7:54-60) He then went on a rampage, hunting down the Christians for official prosecution. Until, that is…Jesus met him in person, and turned him completely around. You can read the story in Acts 9:1-30, and again when Saul repeated it in court in Acts 22:1-21.

Thereafter, Saul — now renamed “Paul” — considered himself to be the apostle sent specifically to the Gentiles, while the others focussed primarily on Jewish audiences. His letters constitute much of the New Testament. Their salutation is often from “Paul, called as an apostle of Jesus Christ by the will of God” (1 Corinthians, Galatians, Ephesians, Colossians, 1 Timothy, Titus). Apparently, he was still sometimes considered a bit suspect, because his letters would emphasize his justification for having the authority of an apostle (1 Corinthians 9:1-2, 1 Corinthians 15:8-10, 2 Corinthians 12:11-12, 1 Timothy 2:7).

The New Testament, the Records of the Apostles

A couple of generations later, when none of the original apostles were left, it became necessary to identify which written materials would be considered authoritative Scripture. The major criteria used was that it must be written by one of the apostles, or someone very close to them ².

Additional Apostles

The title “apostle” was also occasionally used for others besides the Twelve and Paul. Acts 14:14-15 refers to “the apostles Barnabas and Paul“; Ephesians 4:11-13 lists workers that God selected for the church: “some as apostles, and some as prophets, and some as evangelists, and some as pastors and teachers“. As used by Christians today, the capitalized title “Apostle” nearly always means the original men with authority that came from being directly commissioned by Jesus.

Today, Christians don’t use the term “apostle” to refer to ourselves. However, we kind of are apostles: We are all still called to be ambassadors for Christ. We are to deliver His message of love and salvation to the world, regardless of our rank or title!

1. See more in these articles.
2. The other criteria were widespread acceptance by the churches, and consistency with the rest of Scripture. See more detail here and here.