[Taken from TBC Q&A July 1986]:
Question: When the Scriptures talk about "self," what do they mean?
Response: The Bible doesn't give a definition for self [but] it tells us some things about self. Look at Luke:9:23, where Jesus says, "If any man will come after me, let him deny himself, and take up his cross daily and follow me." Self, independent of God, must be denied. That includes my will and everything that I am. Jesus said that I must even hate my life--I must lose my life in order to gain it. If I cling to my life I'll lose it, but if I give it up I'll find a new life. We were made "in the image of God" (Gn 1:27). We're like a mirror. It has one purpose: to reflect a reality other than its own. What would you think of a mirror that tried to develop a "good self-image"?
We are to reflect the image of Jesus as the Holy Spirit empowers us. Matthew:16:24-26 says the same thing.
Jeremiah:10:23 is a powerful scripture that every Christian should memorize: "O LORD, I know that the way of man is not in himself: it is not in man that walketh to direct his steps." We are made in the image of God. That means we are not self-contained, and it's the power and the life of God that is to be lived through us. And when we try to be self-contained entities we are in rebellion to God's design for us.
Even the personalities within the Trinity do not operate independently. Jesus said in John:5:30 that as a man on this earth "I can of mine own self do nothing." John:16:13 says that even the Holy Spirit "shall not speak of himself [i.e., independently of the other members of the Trinity]; but whatsoever he shall hear that shall he speak...." If He will not act independently, then how can we possibly act independently of Him?
So, this "self," which He wants us to deny, attempts to act independently of God.