But that is not the way you learned Christ! — assuming that you have heard about him and 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 4:20-24
What does it mean to "put off your old self"? We may call it the old man, the carnal nature, the adamic nature, the flesh, but the simplest description is just self — me. We are born into the world with a self. We are not blank slates. Anyone who has a child, or more than one, will tell you they are born being different. Self is not personality though the two are related. The persona is our mask, our inter-face as opposed to our intra-face. It is the template or the jig on which we build our relationships with others. Self will be seen — or at least glimpsed from time to time through that template. Some of us are simple and our interface reflects largely and accurately the underlying self. Others of us, either because we are fearful of exposing our nature or perhaps because of the circumstances of our upbringing, have a mask that exposes much less of that nature.
Religions and philosophies have long recognized that self is somehow at the root of many of our problems. Though a Christian, I am rather sympathetic toward Zen, and I think zazen meditation can be practiced by Christians without conflict. I am not sure where this quote came from, but I like it: To study the Buddha Way is to study the self, to study the self is to forget the self, and to forget the self is to be enlightened by the ten thousand things. I suspect generally that what most Zen practitioners are forgetting is a version of the persona rather than the actual self, but the point is still to perceive and experience as directly as possible the pure reality around us. What the truly enlightened will realize is that self cannot be overcome by self.
The key to understanding and ultimately freeing ourselves from self's bondage is to realize it is "corrupt through deceitful desires". We are unable to see things clearly. Our perception is clouded and corroded to the point that we misunderstand, misjudge, and miss the mark. So much that we see in the world is deception. People are drawn into all kinds of suffering because they are deceived. The old nature has no resistance to corruption. Let's go back to the Old Testament for an illustration:
King Solomon made 200 large shields of beaten gold; 600 shekels of gold went into each shield. And he made 300 shields of beaten gold; three minas of gold went into each shield. And the king put them in the House of the Forest of Lebanon. ... In the fifth year of King Rehoboam, Shishak king of Egypt came up against Jerusalem. He took away the treasures of the house of the Lord and the treasures of the king's house. He took away everything. He also took away all the shields of gold that Solomon had made, and King Rehoboam made in their place shields of bronze, and committed them to the hands of the officers of the guard, who kept the door of the king's house. (1 Kings 10:16-17, 14:25-27)
Gold is, of course, incorruptible. Bronze, while quite strong and initially as shining and bright as gold, develops, over time, a patina of corrosion. To keep the shields of Rehoboam looking like gold required a great deal of work, a lot of burnishing and polishing. In the same way, the flesh is resilient and tough. It, too, can be shined up to look pretty good, but it lacks the value, quality, and incorruptible nature of gold. The bronze shields were a counterfeit of the gold shields. Rehoboam, through disobedience, lost a great treasure to Shishak — as king of Egypt, a type of Satan. To avoid being embarrassed by such a loss, he took what he had and made something that served the purpose and "looked just as good" as the shields he had lost.
In Adam, humanity lost the intimate connection with the Father also through disobedience. Like Rehoboam, we were plundered by Satan. From the Fall until the Cross, most of us had little choice except to rely on the self, to do the best we could with what we had, to brush and polish the tarnished face of our old nature and make it as acceptable as we could. The Law gave us the means to keep our shields bright and strong, but what God wanted was for us to have a new and incorruptible nature. The death of Christ and the shedding of His blood provided us with a new covenant. The Cross offered us a way to set aside self and take up a new nature, that of Christ Himself.
The beauty of this new self is that the world is unable to tarnish it. Those "deceitful desires" that assail us can longer cause corruption. Instead of being confused, accused, and harassed, our minds are renewed and refreshed, able to perceive clearly. Now, like those golden shields of Solomon, we reflect back to God His glory, undiminished and unclouded by the corrosion and dust of the world.
In all circumstances take up the shield of faith, with which you can extinguish all the flaming darts of the evil one — Ephesian 6:16