Why did Jesus call apostles?
Jesus had a large circle of disciples around him, both men and women. From this circle he selected twelve men whom he called apostles (Lk 6:12-16). The apostles were specially trained by him and entrusted with various commissions: "He sent them out to preach the kingdom of God and to heal" (Lk 9:2). Jesus took only these twelve apostles with him to the Last Supper, where he gave them the command, "Do this in remembrance of me" (Lk 22:19b).
The apostles became witnesses of Jesus' Resurrection and guarantors of the truth about him. They continued Jesus' mission after his death. They chose successors for their ministry: the bishops. To this day, the successors of the apostles exercise the authority conferred by Jesus: They govern and teach and celebrate the liturgy. The cohesiveness of the apostles became the foundation for the unity of the Church (apostolic succession). Preeminent once again among the Twelve was Peter, on whom Jesus bestowed special authority: "You are Peter, and on this rock I will build my Church" (Mt 16:18). From Peter's special role among the apostles developed the papal ministry. (YOUCAT question 92)
Dig Deeper: CCC section (551-553) and other references here.
Part 1: The Profession of Faith (26 - 1065)
Section 2: The Profession of the Christian Faith (185 - 1065)
Chapter 2: I Believe in Jesus Christ, the Only Son of God (422 - 682)
Article 3: "He was conceived by the power of the Holy Spirit, and was born of the Virgin Mary" (456 - 570)
Paragraph 3: The Mysteries of Christ's Life (512 - 570)
III. THE MYSTERIES OF JESUS' PUBLIC LIFE ⇡
"The keys of the kingdom" ⇡
From the beginning of his public life Jesus chose certain men, twelve in number, to be with him and to participate in his mission.280 He gives the Twelve a share in his authority and 'sent them out to preach the kingdom of God and to heal."281 They remain associated for ever with Christ's kingdom, for through them he directs the Church: As my Father appointed a kingdom for me, so do I appoint for you that you may eat and drink at my table in my kingdom, and sit on thrones judging the twelve tribes of Israel.282
280.
Cf. Mk 3:13-19.
281.
282.
Simon Peter holds the first place in the college of the Twelve;283 Jesus entrusted a unique mission to him. Through a revelation from the Father, Peter had confessed: "You are the Christ, the Son of the living God." Our Lord then declared to him: "You are Peter, and on this rock I will build my Church, and the gates of Hades will not prevail against it."284 Christ, the "living Stone",285 thus assures his Church, built on Peter, of victory over the powers of death. Because of the faith he confessed Peter will remain the unshakable rock of the Church. His mission will be to keep this faith from every lapse and to strengthen his brothers in it.286
283.
Cf. Mk 3:16; 9:2; Lk 24:34; 1 Cor 15:5.
284.
285.
286.
Cf. Lk 22:32.
Jesus entrusted a specific authority to Peter: "I will give you the keys of the kingdom of heaven, and whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven."287 The "power of the keys" designates authority to govern the house of God, which is the Church. Jesus, the Good Shepherd, confirmed this mandate after his Resurrection: "Feed my sheep."288 The power to "bind and loose" connotes the authority to absolve sins, to pronounce doctrinal judgements, and to make disciplinary decisions in the Church. Jesus entrusted this authority to the Church through the ministry of the apostles289 and in particular through the ministry of Peter, the only one to whom he specifically entrusted the keys of the kingdom.
287.
288.
289.
Cf. Mt 18:18.