An apostle (“one sent on a mission”) is one whom God has sent on an errand or with a message. An apostle is accountable to his Sender and carries the authority of his Sender.
Jesus Christ Himself wears Apostle as one of His descriptive titles (Hebrews 3:1). He was sent to earth by the Heavenly Father with God’s authoritative message, which He faithfully delivered (John 17:1–5).
While Jesus was here on earth, He personally selected from His many followers twelve men and gave them special responsibility to receive and spread His message after He returned to heaven (John 17:6–20; Matthew 10:1–4; Mark 3:14–15; Mark 6:40). These chosen and sent ones were His apostles. During the time Jesus was training them, He did not explain the criteria that He used to choose them. It would be interesting to study the common traits of those twelve men and what might have been Jesus’ qualifications.
One of the twelve was Judas Iscariot, who betrayed Jesus to His enemies. In agony of conscience, Judas hanged himself (Matthew 27:5). Thus, when Jesus returned to heaven, He left behind only eleven apostles.
Some days later, the remaining apostles were praying with Jesus’ mother, His brothers, and other believers. The group totaled about 120 (Acts 1:12–26). Simon Peter addressed the group and told them that Psalm 69:25 predicted Judas’ desertion and Psalm 109:8 predicted that the defector’s place among the apostles should be filled.
Peter proposed choosing a new apostle and set the qualifications. Anyone under consideration needed to have been with Jesus during the whole three years that Jesus was among them. That is, he needed to be an eye-witness of Jesus’ baptism when the Heavenly Father validated Jesus’ person and work. He needed to have heard Jesus’ life-changing teachings and been present to see His healings and other miracles. He needed to have witnessed Jesus sacrifice Himself on the cross and to have seen Jesus walk, talk, and eat among the disciples again after His resurrection. These were the pivotal facts of Jesus’ life, the heart of the message they were to teach, and personal witnesses were required to verify the truth of the good news.
The prayer group nominated two who met these qualifications, Joseph Barsabbas and Matthias. Then the disciples asked God to guide them to know which one was to fill the post. Using a method of determining God’s will that was common at that time, they cast lots, thus giving God freedom to make His choice clear. The lot fell to Matthias, and he became the twelfth apostle.
On repeated occasions, these men gave witness of their personal observations of Jesus, using such words as, “We are witnesses of everything Jesus did in the country of the Jews and in Jerusalem. They killed him by hanging him on a tree, but God raised him from the dead on the third day and caused him to be seen” (Acts 10:39–40).
Months later, Saul, one of the Pharisees, was trying to stamp out the new “cult” of Christianity by killing and jailing some of Jesus’ followers. While Saul was on one of his deadly errands to Damascus, the living Jesus personally appeared to him. This undeniable encounter with the resurrected Lord revolutionized Saul’s life. In a vision to another believer in Damascus, Jesus said that He had chosen Saul “as My chosen instrument to carry My name before the Gentiles and their kings and before the people of Israel” (Acts 9:15; cf. 22:14–15). Following his conversion, Paul spent some time in Arabia, where he was taught by Christ (Galatians 1:12–17). The other apostles recognized that Jesus Himself had appointed their former enemy to be one of them. As Saul went into Gentile territories, he changed his name to the Greek “Paul,” and Jesus sent many messages through him to His churches and to unbelievers. It was this apostle, Paul, who wrote over half of the books of the New Testament.
In two of his Epistles, Paul identifies the office of apostle as the first that Jesus appointed to serve His churches (1 Corinthians 12:27–30; Ephesians 4:11). Clearly, the work of the apostle was to lay the foundation of the Church in a sense secondary only to that of Christ Himself (Ephesians 2:19–20), thus requiring eye-witness authority behind their preaching. After the apostles laid the foundation, the Church could be built.
While Paul never claimed to be included among the original twelve, he, the others, and all believers have recognized that Jesus appointed him as His special apostle to the Gentiles (Galatians 1:1; 1 Corinthians 9:1; Acts 26:16–18). There are others in the early church referred to as “apostles” (Acts 14:4, 14; Romans 16:7; 1 Thessalonians 2:6), but only in the sense that they were appointed, authorized, and sent by churches on special errands. These individuals bore the title in a limited sense and did not possess all the qualifications of apostleship that the original twelve and Paul did.
No biblical evidence exists to indicate that these thirteen apostles were replaced when they died. See Acts 12:1–2, for example. Jesus appointed the apostles to do the founding work of the Church, and foundations only need to be laid once. After the apostles’ deaths, other offices, not requiring an eye-witness relationship with Jesus, would carry on the work.
 Got Questions Ministries. (2010). Got Questions? Bible Questions Answered. Bellingham, WA: Logos Bible Software.