An apostle, derived from the Greek word apostolos, signifies a delegate, envoy, agent, ambassador, or representative, one sent with a special message or commission. This commission may be for a specific errand or extend over a lifetime. In the Jewish context, an apostle, or shaliah, represented individuals or bodies like courts and synagogues, tasked with duties such as serving legal documents, collecting monies, or conveying instructions. The principle was that a man's shaliah is like himself, identifying the one who authorized and sent him through faithful execution of instructions. In the New Testament, the usage of apostle takes on a religious, institutional, and missionary character. Jesus Christ, described as the Apostle and High Priest of our confession, was faithful to Him who appointed Him, fulfilling His commission so completely that He declared, "He who has seen Me has seen the Father." Following this pattern, Jesus appointed twelve to be with Him and sent them out to preach, heal sicknesses, and cast out demons, representing Him as His apostles. He stated, "As the Father has sent Me, I also send you," implying that those sent are chosen by divine will for their mission, bearing His authority. Beyond the Twelve, others like Paul, Barnabas, and Jesus' brothers James and Jude are named as apostles in scripture. Their appointments often involved ordination by church officers under the direction of the Holy Spirit, as seen with Barnabas and Saul, who were set apart for a specific work and sent out. Paul defended his apostleship by pointing to visible signs such as preaching the gospel of the Kingdom of God, healing, casting out demons, converting people, raising congregations, and clarifying doctrine under Christ's guidance. The function of an apostle, therefore, is to act as a direct representative of the one who sent him, carrying out a divine mission with authority. This role includes preaching, performing signs and wonders, and establishing and guiding congregations, as evidenced by the fruits of their ministry.

The function of the apostle is introduced within Paul's broader discussion of the ministry as a gift Christ gave to the Church, as recorded in Ephesians 4:11, where apostles are named first among the five ministerial offices—apostles, prophets, evangelists, pastors, and teachers. This placement is significant, since being listed first suggests apostles hold one of the most important roles among these gifts. The word "apostle" itself means envoy or ambassador, someone who has been sent with a specific mission to fulfill. This definition establishes the apostle's essential function: he is a messenger, one entrusted with a task and dispatched to carry it out on behalf of another. This distinguishes the apostle from the prophet, who serves as a spokesman; from the evangelist, who spreads good news; from the pastor, who shepherds a flock; and from the teacher, who instructs. Though some overlap exists among these ministerial roles, each retains a distinct primary function, and the apostle's defining characteristic is that of being sent as an ambassador carrying a message. This apostolic function connects directly to the larger purpose for which Christ gives gifts to men, described in Ephesians 4:7-8, where Christ, having ascended and led captivity captive, distributes spiritual gifts necessary for believers to be equipped and ultimately joined with Him. The apostle, like the other ministerial gifts, exists for the equipping of the saints and the edifying of the body of Christ, working toward the goal that the whole Church come to the unity of the faith, the knowledge of the Son of God, and the measure of the stature of the fullness of Christ. Thus, the apostle's mission-driven role serves the same ultimate aim as all ministry: to prepare believers for service and to build up the Church into the image of Christ. Peter is presented as an example of this apostolic function in action. In John 21:15, he is identified as "the chief apostle and one of the first ministers of the New Testament Church," and Christ's charge to him—"feed my lambs," "tend my sheep," "feed my sheep"—illustrates the fundamental responsibility placed upon apostles and all ministers: to provide spiritual nourishment and to shepherd, guide, protect, and, when necessary, discipline the flock. This exchange reveals that the apostolic mission, though defined by being "sent" with a message, is carried out through love for Christ and for His flock, expressed practically through feeding and tending God's people. In this way, the function of the apostle is woven into the larger message concerning the ministry's role in helping believers discern truth from error during the end times. As an envoy sent with a divine message, the apostle serves as one of the human instruments through which Christ, working by His Spirit, equips and matures the Church, guarding it against deception and leading it toward unity, spiritual growth, and ultimately the fullness of Christ.

The function of apostles emerges directly from Christ's declaration in Matthew 16 that He would build His church, giving the apostles the keys of the Kingdom of heaven, with the promise that whatever they bound on earth had already been bound in heaven. This indicates that the apostles were to work within the framework of God's law, while Christ Himself, being alive through resurrection, would continue to inspire, lead, and guide them in the conduct of the church. This ongoing inspiration did not mean apostles were incapable of error; rather, Christ remained able to correct them because they, like all people, had to learn through experience. Peter's rebuke of Jesus for predicting His own death illustrates this fallibility clearly. Though Peter had just been given a position of responsibility, he was still influenced by a materialistic, nationalistic perception of the Messiah shared by the Jews of his day, and his attempt to dissuade Christ from suffering paralleled Satan's earlier temptations of Christ in the wilderness—both offered materialistic, man-centered alternatives to God's plan. Jesus rebuked him sharply, calling him "Satan" not because Peter was possessed, but because he had been influenced by that same materialistic spirit, being "not mindful of the things of God." Yet Christ's correction, "Get behind Me," differed from His words to Satan; it was a call for Peter to return to his proper place as a follower rather than a leader attempting to redirect Christ's mission. This same flawed, human perception of the Messiah's role is suggested as a possible factor behind Judas's later actions, showing that apostleship did not exempt one from serious misjudgment when human reasoning overrode submission to God's will. The function of the apostles also included being witnesses prepared to strengthen and lead others. Peter, James, and John were specifically taken up the mountain to witness the Transfiguration, receiving a vision of Christ glorified in His Kingdom alongside Moses and Elijah. This experience gave these three men an extra measure of assurance and vision of the Kingdom that set the pace for the other apostles, equipping them to endure the trials ahead. Peter later referred back to this event as being an "eyewitness of His glory," underscoring how firsthand experience of Christ's glory became foundational to apostolic leadership and testimony. Ultimately, the proper functioning of an apostle depended on first possessing a correct perception of who Christ truly was—something neither the Jewish leaders nor even His own disciples fully grasped until after the resurrection, when they received God's Spirit. This underscores that apostleship required more than proximity to Christ or position of authority; it required Spirit-given revelation, correction from Christ Himself, and submission to God's plan rather than human, materialistic solutions, before the apostles could genuinely represent Him and build up the church He was establishing.