I believe that there is an old adage that states that it is not where you start but where you finish that matters. I also believe that I could have just made that up because it sounds good, but I still think it is a valid point.
If you start in ignorance and end in ignorance then shame on others if they did not teach you or shame on you for not listening! If you start in sin you should not end in your sin because we have the Truth of Christ proclaimed and lived all around us.
Peter started out poorly, but when the lessons came, he took them to heart. Not only that but he recognized his whole life how easy it is to slip back into old patterns of sinfulness and worked to do better by doing good. Mark Twain had a saying about some of the missionaries to Hawaii: they came to do good and did well. Peter started out to do well and in the end did good.
Through humiliation he learned humility; through temptation he learn prudence and charity. He may have started out selfish, vain, and greedy but he ended up a true servant of Christ to king and shepherd alike. Peter reminds us that our true discipleship begets true discipleship in others.
Beatified but never officially canonized, Benedict the XIV formally recognized the devotional culture dedicated to him, so you will see him alternately designated as "saint" or "blessed".
As the number of disciples continued to grow, the Hellenists complained against the Hebrews because their widows were being neglected in the daily distribution. So the Twelve called together the community of the disciples and said, "It is not right for us to neglect the word of God to serve at table. Brothers, select from among you seven reputable men, filled with the Spirit and wisdom, whom we shall appoint to this task, whereas we shall devote ourselves to prayer and to the ministry of the word." The proposal was acceptable to the whole community, so they chose Stephen, a man filled with faith and the Holy Spirit, also Philip, Prochorus, Nicanor, Timon, Parmenas, and Nicholas of Antioch, a convert to Judaism. They presented these men to the Apostles who prayed and laid hands on them. The word of God continued to spread, and the number of the disciples in Jerusalem increased greatly; even a large group of priests were becoming obedient to the faith.
-- Acts 6:1-7