Now that we have found that apostles are men who have been commissioned and that this concept applies to many more people in the NT than only to "the twelve" and Paul, the question arises: What is so special about "the apostles"? The answer is: They are "apostles of Christ" (2Cor.11:13; 1Thes.2:6; see also: 1Pet.3:2; Jude 1:17), that is to say, they have been personally commissioned by Him, Who by virtue of His resurrection is the Christ (Acts 2:36).
In his letter to the Corinthians, Paul tells of the many appearances of Christ, from the time of His resurrection, and writes:
5 and that He was seen by Cephas, thereupon by the twelve.
6 Thereupon He was seen by over five hundred brethren at once, of whom the majority are remaining hitherto, yet some were put to repose also.
7 Thereupon He was seen by James, thereafter by all the apostles.
The distinction that is made here between "the twelve" and "all the apostles" is an indication that the circle of apostles is wider than "the twelve". That is correct, because in Luke 10:1 mention is made of yet seventy-two other men, in addition to the twelve, who were dispatched (Gr. apostello > apostle) with full authorization. To these, apparently, also belonged Barnabas (Acts 4:36) since he later, as well as Paul, is called an apostle (Acts 14:14; see also 1Cor.9:6 and Gal.2:9). This also applies to Silas/Silvanus, whom Paul also reckons to be an apostle (1Thes.1:1 and 2:6). But Paul's words also imply something else, namely, that "all the apostles" are eyewitnesses of the risen Christ. And that also explains Paul's rhetorical question in 1 Corinthians 9:1:
Am I not an apostle? Have I not seen Jesus our Lord?
When in Acts 1, the vacancy of Judas must be filled, then there is a requirement demanded of the candidates, that they not only, from the beginning had been a disciple, but also are eyewitnesses of the risen Christ (Acts 1:22).
However, Paul is an apostle of Christ in a special sense, because he was called at a time when the company of apostles was complete and Christ had already, for a number of years, left this (terrestrial) stage. Paul, according to his own statement, is the final apostle:
8 And LAST OF ALL (namely, of all the apostles; see verse 7) he was seen of me also, as of one born out of due time.
9 For I am the least of the apostles, that am not meet to be called an apostle, because I persecuted the church of God.
-1 Cor.15- (KJV)
Because Paul, from out of heaven was called by Christ, the earthly Jesus kind of disappeared into the background with him (cf 2Cor.5:16). Almost without exception, he therefore introduces himself, in his letters, as "apostle of Christ Jesus." Christ is first with him, because from that position Paul has gotten to know Him. By starting his letters with, "apostle of Christ Jesus", he legitimizes his authority, because He is commissioned and authorized by the risen and glorified Christ Himself.
Translation: Peter Feddema