JC - Chapter 16

Luke records that -

"...it came to pass in those days, that he went out into a mountain to pray, and continued all night in prayer to God.
13 ¶ And when it was day, he called unto him his disciples: and of them he chose twelve, whom also he named apostles;
14 Simon, (whom he also named Peter,) and Andrew his brother, James and John, Philip and Bartholomew,
15 Matthew and Thomas, James the son of Alphæus, and Simon called Zelotes,
16 And Judas the brother of James, and Judas Iscariot, which also was the traitor."  (New Testament | Luke 6:12 - 16)

Mark would record that -

"...he ordained twelve, that they should be with him, and that he might send them forth to preach..."  (New Testament | Mark 3:14)

Obviously, from his disciples or followers that believed, the Savior set apart and ordained twelve with special power and responsibilities.  I note that He did this under guidance and inspiration as He prayed "all night".  The apostleship brought with it a special responsibility and witness of the Savior.  It was this set apart quorum that was taught and trained and that would lead His Church after the Savior departed.  This quorum is evidence of the Lord's intention to lead His Church...a sign of the true Church.

Talmage wrote -

"Discipleship is general; any follower of a man or devotee to a principle may be called a disciple, The Holy Apostleship is an office and calling belonging to the Higher or Melchizedek Priesthood, at once exalted and specific, comprising as a distinguishing function that of personal and special witness to the divinity of Jesus Christ as the one and only Redeemer and Savior of mankind. The apostleship is an individual bestowal, and as such is conferred only through ordination. That the Twelve did constitute a council or “quorum” having authority in the Church established by Jesus Christ is shown by their ministrations after the Lord’s Resurrection and ascension. Their first official act was that of filling the vacancy in their organization occasioned by the apostasy and death of Judas Iscariot; and in connection with this procedure, the presiding apostle, Peter, set forth the essential qualifications of the one who would be chosen and ordained, which comprised such knowledge of Jesus, His life, death, and Resurrection, as would make the new apostle one with the Eleven as special witnesses of the Lord’s work.

The ordination of the Twelve Apostles marked the inauguration of an advanced epoch in the earthly ministry of Jesus, an epoch characterized by the organization of a body of men invested with the authority of the Holy Priesthood, upon whom would rest, more particularly after the Lord’s departure, the duty and responsibility of continuing the work He had begun, and of building up the Church established by Him.

The word “apostle” is an Anglicized form derived from the Greek apostolos, meaning literally “one who is sent,” and connoting an envoy or official messenger, who speaks and acts by the authority of one superior to himself. In this sense Paul afterward applied the title to Christ as one specially sent and commissioned of the Father.

The Lord’s purpose in choosing and ordaining the Twelve is thus enunciated by Mark: “And he ordained twelve, that they should be with him, and that he might send them forth to preach, and to have power to heal sicknesses, and to cast out devils.”  For a season following their ordination the apostles remained with Jesus, being specially trained and instructed by Him for the work then before them; afterward they were specifically charged and sent forth to preach and to administer in the authority of their priesthood, as shall be hereafter considered."