The Greek word apostolos (“someone who has been sent”) is seldom used in classical Greek, but it occurs eighty times in the New Testament, where it means “delegate” of Jesus Christ and “messenger” of the gospel. Paul lists apostles first among the members of the body of Christ (1 Cor. 12.29; cf. Eph. 4.11).
The corresponding word in Hebrew (šālîaḥ) was especially used to denote someone given full authority, for some particular purpose and for a limited time, to represent the person or persons from whom the delegate comes; the rabbis said that “a man's šālîaḥ is as himself.” The legal status of such a delegate has its roots in Semitic customs pertaining to a messenger (see 1 Sam. 25.40; 2 Sam. 10.1–5). The mission of Paul to Damascus (Acts 9.1–2) and the delegation of Barnabas and Paul by the church of Antioch (Acts 11.30; 13.2; see 14.4, 14) are to be understood in terms of a rabbinic šālîaḥ. The same holds true for the sending of the disciples by Jesus, who included the “apostles” (Mark 3.14 par.). They went two by two (Mark 6.7; Luke 10.1); their task of proclaiming the gospel and casting out demons was limited as to sphere and time (Matt. 10.5–8), and they had to return to the sender and report about their task (Mark 6.30; Luke 10.17).
Although Jesus is called “apostle” only once in the New Testament (Heb. 3.1), in his “Son of man” sayings he presents himself as the agent of God for salvation (Mark 2.17; 10.45; Luke 5.32; 7.34; 19.10; see also Matt 10.40). The divine commission of the Son is elaborated in the gospel of John, where the evangelist more than once uses the law concerning the authority of the S̆ālîaḥ (7.33; 16.5; 17 passim).
The status of a post‐Easter apostle of Christ transcends that of a Jewish šālîaḥ. In his letters, Paul often defends and defines his apostolic authority. He mentions the apostles before him (Gal. 1.17), specifying Peter, the twelve, James, and all the apostles (1 Cor. 15.5, 7). Though Paul was called last of all and considered himself to be the least of them (1 Cor 15.8–9), he was convinced that God had set him apart before he was born (Gal. 1.15); thus, Paul repeated the claim of the prophet Jeremiah (1.5) and of the servant of the Lord (Isa. 49.1–5). This means that the apostles of Christ had to serve during their whole lives as did the biblical prophets, who were called by God and spoke as his messengers. Paul may have used the narrative of Isaiah's call as a key for interpreting his vision near Damascus. The motifs of Isaiah 6 can be discovered in scattered statements in which Paul speaks about the call and about the nature of his apostleship. The rhetorical questions “Am I not an apostle? Have I not seen Jesus our Lord?” (1 Cor. 9.1) get their force from Isa. 6.1, 8: “I saw the Lord … send me!” Moreover, Paul understood his call to apostleship as an act of the grace of God (Rom. 1.5). As a persecutor of the Christians he was not worthy of it (1 Cor. 15.9); in a similar way, Isaiah had confessed his unworthiness (6.5–7). Isaiah had been told to bring a message of doom to the Israelites that would harden them (6.8–10); Paul experienced disobedience to the gospel by his fellow Jews (Rom. 10.16; 11.7–10), which is why he brought it to the gentiles (see Acts 28.25–28). He felt the necessity to preach his message (1 Cor. 9.16) as Jeremiah had (20.9).
Besides the limited group of apostles (the twelve) in Jerusalem (1 Cor. 15.5, 7; Gal. 1.17, 19), Paul knew another circle of apostolic preachers (1 Cor. 9.5; 12.28; 2 Cor. 11.13; Rom. 16.7). Therefore, one may distinguish between two types of New Testament apostles in Paul's view: those called through an appearance of the risen Lord; and charismatic preachers, who were delegated by a church such as that at Antioch (see Acts 13.1–3; Rev. 2.2; Did. 11.3–6), including both men and women (Rom. 16.7; See Junia). But both types were united in a figure such as Paul. On the other hand, Luke reserves the designation “apostle” for the twelve disciples of Jesus who became the leaders of the Jerusalem church. For him, the apostle has to be a companion of Jesus and a witness to the resurrection (Acts 1.21–22). This seems to be the view of Mark (6.30; see 6.7) as well as that of Matthew (10.2).