Wilber T. Dayton. “Factors promoting the formation of the New Testament canon” in Bulletin of the Evangelical Theological Society 10.1 (Winter 1967): 28-35. See p. 30-31.
Geldenhuys, J. Norval. Supreme Authority: The Authority of the Lord, His Apostles, and the New Testament. Eermands, 1953. See p. 48-61, 68, etc.
Liftin, Bryan M. After Acts: Exploring the Lives and Legends of the Apostles. Moody, 2015, 199 pages. See p. 13-14.
“The word apostolos comes from a Greek verb meaning ‘to send out.’ In the original culture of ancient Greece, an apostle was just a sailor sent across the sea with no particular authority. Eventually the word came to mean a messenger or delegate. First-century Judaism had its own Hebrew word for an official envoy who was commissioned to proclaim a precise message and who therefore possessed special authority—the shaliah. This seems to be the meaning behind the Greek word apostolos as it is used in the New Testament…Normally, an apostle was someone wo had been diectly commissioned by Jesus Christ to proclaim the message of His saving death and resurrection.”