The time came in Jesus’ ministry when the crowds of would-be followers were growing so large that Jesus decided to organize a core group of disciples. As Dr. Bruce observes, Jesus’ teaching was “beginning to be of a deeper and and more elaborate nature, and His gracious activities were taking on an ever-widening range.”
Here is the central theme of The Training of the Twelve: “It was impossible that all who believed could continue . . . to follow Him, in the literal sense, whithersoever he might go: the greater number could now only be occasional followers. But it was His wish that certain selected men should be with Him at all times and in all places,--His travelling companions in all His wanderings, witnessing all His work, and ministering to His daily needs. “He appointed twelve—designating them apostles—that they might be with him and that he might send them out to preach” (Mark 3:14 NIV).
“They were to be . . . students of Christian doctrine, and occasional fellow-laborers in the work of the kingdom, and eventually Christ’s chosen trained agents for propagating the faith after He Himself had left the earth. From the time of their being chosen, indeed, the twelve entered on a regular apprenticeship for the great office of apostleship, in the course of which they were were to learn, in the privacy of an intimate daily fellowship with their Master, what they should do, believe, and teach, as His witnesses and ambassadors to the world”
(The Training of the Twelve by A.B. Bruce, published by Kregel Publications, in 1971, Reproduced from the fourth edition by A.C. Armstrong and Son, 1894. Foreword by D. Stuart Briscoe, copyright 1988 by Kregel Publications. Chapter 1 Beginnings, pages 29—30).