“Discipline, so conceived, is something that the Christian church lacks in our time. It is high time that we all recognize that God requires us to discipline ourselves by constant practice in obeying His revealed will and this exercise (train) ourselves toward godliness.
Practically speaking, what does this involve? In Luke 9:23, Jesus commands His disciples: ‘Take up your cross daily,’ denying the self. He does not mean denying yourself something. There is no idea of penance in this. ‘For Lent I’ll stop chewing gum,’ says the penitent. That is exactly not what is in view. Rather, Jesus insisted that Christians must deny the self within them. By the old self, He meant the old desires, the old ways, the old practices, the old habit patterns that were acquired before conversion. They became so much a part of day-by-day practice that they became second nature. We were born sinners, but it took practice to develop our particular styles of sinning, the old life was disciplined toward ungodliness. That is why Paul says that the believer must daily deny (literally say ‘no’ to) the self.
Daily denial of the self indicates the presence of a day-by-day battle inside of the Christian. He must ‘take up the cross’ as an instrument of death upon which to crucify the self every day. Taking up the cross doesn’t mean carrying some heavy burden. It is not enduring trial (‘I guess my cross is that I must live the rest of my life with my wife’). No, that isn’t what is in view at all. Taking up the cross means going to the place of death. It means putting to death the old life patterns of the old man.
But that is not enough. Whenever God says ‘put off’ He also says ‘put on’. On the positive side, each day one also must seek to ‘follow’ Jesus Christ. That is what it means to discipline oneself for godliness. It means to continue to say ‘no’ to self and ‘yes’ to Christ every day until one by one all of the old habitual ways are replaced by new ones. It means that by daily endeavor to follow God’s Son, one finds at length that doing so is more ‘natural’ than not doing so. The Holy Spirit thus enables a believer to put off the old man and put on the new man.” – Jay Adams, Godliness Through Discipline