At that time we lived as the Gentiles live, as the world lives, and now we look back amazed at our rash behaviour in inviting the judgment of God. His use of the word Gentiles is not intended to re-establish the distinctions of the Old Testament between Jew and Gentile, but to remind his readers what is the only state of human beings outside of the fold of God.
If it is true that he who is forgiven much loves much, then it is a good thing for us to be reminded how we used to live. This is not said to fill us with guilt all over again as if God still remembered our sins against us, but to help us to appreciate the great gift we have received from him in having our debt cancelled. We should not keep re-confessing the same sins, but we give thanks to God for the fact that he has pardoned those sins. We cannot deny our past and nor should we try to forget it, for it is part of the history of grace in our life-story. Sin has been allowed by God to come into existence in order that his grace should be exalted to the highest degree. It is a spur to our progress in holiness that we have wasted so much of our past life in foolish disobedience. The believer may take revenge on his past life by living such a markedly different life, for he remembers with regret what he was, and turns that regret to advantage.
The Christian makes no attempt to mitigate his past evil life, for he has received a free pardon, and this was given on condition that he admit the full extent of his sin. If God had not been aware of all that he did in the past then forgiveness would not have been possible. Having been forgiven, why should he try to hide it, for what is to his own dishonour is to the glory of God to whom he owes everything, and Peter includes himself with his readers as one who lived in excess in the past.
You walk in lasciviousness every time you go to a Hollywood movie, which is full of sex. You are letting your guard down; you are letting your mind be polluted. There are Christian people and they have the right profession. Then they get married and people tell me, ‘Oh, the reception. There was a band there, and the world's music, and there was dancing, and you couldn't have easily told the difference between this and a worldly wedding. And yet we thought that young couple had done with the world, finished with the world, and now we find them up to the neck in the world, because they are not prepared to be scorned by all their worldly friends.