"[You] were taught in him, as the truth is in Jesus, to put off your old self, which belongs to your former manner of life and is corrupt through deceitful desires, and to be renewed in the spirit of your minds, and to put on the new self, created after the likeness of God in true righteousness and holiness." (Ephesians 4:21-24 ESV)
"The whole matter of putting on the new man is in essence the application of truth to ourselves. It is the most important thing that one can ever discover in the Christian life. The real secret of Christian living is to discover the art of talking to yourself. We must talk to ourselves, we must preach to ourselves, and we must take truth and apply it to ourselves, and keep on doing so. That is the putting on of the new man. We have to hammer away at ourselves until we have really convinced ourselves. In other words, this is not something that you wait for passively. If you wait until you feel like the new man it will probably never happen. We must be active in this. There is no greater snare in the Christian life than to entertain the idea of waiting until we feel better, and of then putting on the new man. On the contrary, we have got to go on telling ourselves the new man is already in us. In his Epistle to the Romans the Apostle Paul says, 'Reckon yourselves to be dead indeed unto sin, and alive unto God' (6:11). Reckon yourselves! Say it to yourself! Persuade yourself, argue, say it to yourself, announce it to yourself. The moment you wake up in the morning say to yourself, I am the new man in Christ Jesus, I am not the old man, I do not belong to the world, I belong to God, I belong to Christ. That is the truth about you whatever your feelings may be.
~ Martyn Lloyd-Jones, Darkness and Light, pp 191-192.