It is important to notice that in all these three cases, vocation was for a mission of salvation and that for God the sins and the fragility of the three called had not been an obstacle to His call. He forgave them, purified them, and gave them the strength for the task.
All of them received the peace of forgiveness and became missionaries among men. They became spokespersons of God and of His Kingdom, that is a kingdom of freedom, justice, truth, peace and above all of love.
For Isaiah who welcomed the divine cry "Whom shall I send? Who will go for us?" God changed the heart so that he could answer "Here I am, send me!" The great prophet could answer in this way because the Seraphim had purified his lips with burning coal. This angelic deed is the consequence of the fact that Isaiah had encountered God and had recognized his condition as a sinner.
Christ gave to Paul His grace and told him "I have appeared to you for this purpose, to appoint you as a servant and a witness of what you have seen [of me] and what you will be shown." (Acts, 26 16b) For the Apostle of the Gentiles the encounter with the Lord was the condition to change the meaning of his life and to live it as a mission. From rabid persecutor Paul became tireless announcer of Christ.
To Peter, Jesus gave strength strong as a stone so that the first among the apostles could follow Him without giving in. As a co-star of the miraculous catch of fish, Peter had said to Jesus "Depart from me, Lord, for I am a sinful man. I'm not worthy to have a Saint in my boat" ( Lk 5,8). The Redeemer answered "Do not be afraid; from now on you will be catching men."(Lk 5:10) That humble fisherman of Galilee became the one who fished men, lifting them from the water poisoned by sin and plunging them in the water purified by God's love.
Life as a vocation
The astonishment of the miracle, the words and above all the encounter with Christ invaded not only Peter, but also all the ones who were with him fishing and in particular his brother Andrew and his partners James and John.
Jesus wasn't alone any more. Four men, two pairs of brothers who became even more brothers because of the common faith, abandoned everything, their job and their families to become companions of Christ. Four humble fishermen, four workmen who, if not illiterate, definitely were not doctors, had been called by Jesus to share His mission as the savior of the human family.
Why did these fishermen leave everything to follow this Man who was promising neither money nor glory and was speaking "only" about love, perfection, poverty and joy ("Blessed be the poor because they will be the Kingdom of Heaven")?
They left everything because God had become the affective center of their life and only He had words of eternal life. He is the Life of life. The encounter with Christ impacted their insignificance. The discovery of Christ as the center of everything erased every fear. They proved to them that the one who follows Christ doesn't walk in darkness and they put themselves at the service of the Kingdom of God. They followed Christ and lived in community with Him, who in a parable described himself as the Good Shepherd. In this parable charity manifests itself in all its full capacity of initiative, creativity, and strength. ( LK 15:4-6)
The Apostles accepted life as a vocation and Christ's mission became their vocation.
The profound availability to put their life at the service of Christ's love was essential to understand their personal vocation. That is not the case of Zacchaeus. (Today's gospel in the Ambrosian Rite) ( Lk 19:1-10)
Zacchaeus was only curious to see Him, and didn't have any intention whatsoever to be close to Christ because, being a publican, he was considered a sinner. He didn't know that Christ had come to call the sinners, to give them a vocation that is the proposal to be with him and share his life and his mission. In the day when Christ was going by Jericho, this man, very attached to money, had climbed a tree to see the Messiah.
For him that day was not an ordinary day. It was the day of the encounter between him and Christ who, looking at him with love (Christ loves the sinners. He has come for them and for us) said to him "Today I must stay at your house". Perhaps Christ had thought of him when He told the parable of the Pharisee and the Publican who didn't dare to lift his eyes, was ashamed to be in front of the Lord, to be seen, was beating his chest and was able only to say "God, have pity on me because I'm a sinner".
Perhaps in Zacchaeus the question of forgiveness was implicit in the request to see Jesus. The rest was done by God whose look saves. Christ's look goes beyond appearances and sees the heart that hopes for the resurrection. He doesn't ask to Zacchaeus "What did you do?" He doesn't reproach his sins. He calls him to be his guest. Zacchaeus understands that it is a call to be in communion with Christ.
It is natural that this man put himself at the disposal of the Man God and of His messianic mission. This publican "welcomes Jesus with joy" because Christ's invitation had given new and true meaning to his life. His neighbor was not any more someone to take advance of, but someone with whom to have a relationship of justice, forgiveness and true fraternity.
Vocation to love in virginity.
This native and fundamental vocation to love typical of any man and of any woman can be fully realized in matrimony and in virginity. These are "two ways to express and to live the unique mystery of the covenant between God and his people" (Familiaris Consortio, # 11)
Matrimony and virginity are not in contrast. They are two different and complementary gifts that converge manifesting the same spousal mystery of the fecund and salvific union between Christ and the Church.
However it is important to remember that in the Church Virginity is the highest vocation. It is the acme of love, the full answer to Christ's predilection, within which one can look at people in the same way Christ looked. Of this love of predilection the Virgins are called to be martyrs (a Greek word that means witnesses), spouses and mothers in spirit, able to give their life with passion so that Christ can be known and the encounter with Him may change one's life.
The Bishop during the Rite of the Consecration of the Virgins urges "Your motherhood will be a motherhood of the spirit, as you do the will of your Father and work with others in a spirit of charity, so that a great family of children may be born, or reborn, to the life of grace" (CV 29). "Our Lord Jesus Christ ( .) may by the strength of his word make your life fecund)" (CV 56). "The Holy Church considers you an elected part of Christ's flock: in you his supernatural fecundity blooms and gives fruit" (CV 29). In this way the consecrated Virgins collaborate in the divine fishing, generating and recuperating many children to the life of grace and love given by Christ.
Is 6:1-2,3-8; Ps 137; 1Cor 15.1-11; Lk 5:1-11