Once we belong to Christ, we begin to crucify the things that don't belong in our lives. Three things are listed here that we must drive out---self, fears, worries. These three things work against our new life in Christ and are things which he died to defeat. Until we drive out self---that worldly master of our life---we cannot instead accept God's will and desire to obey it. The Holy Spirit wants to move in and help us drive out "self" who occupies the place where He wants to live. The self sins must cease to rule in our lives.
A.W. Tozer gives a good list of some of them---"self-righteousness, self-pity, self-confidence, self-sufficiency, self-admiration, self-love." (Tozer---"The Pursuit of God)
"They are not something we do, they are something we are, and therein lies both their subtlety and their power."----Tozer
Some of those "self" aspects sound innocent. We are taught in this world to love our self and to be self-sufficient and have self-confidence. It is all about building a healthy self-image that allows us to deal with the world. While it is good to not hate ourselves and to have the strength of character we need to function and grow mature, it is important to know the source of that strength and that character. We need to build our healthy self-image on God and his love and provision for us. Our character should come from Christ.
When we begin to see all those "self" things as being from our own work and focus all our thoughts on what is best for us, we lose our focus on God. Our righteousness comes from Christ, not us---so strike out thoughts of self-righteousness! We can't make ourselves righteous! Self-pity---feeling sorry for ourselves denies thankfulness to God. We deny his goodness and faithfulness and lose our trust in him. It's "all about us" when we dwell in self-pity. When we dwell instead in an abiding relationship with God, then it is "all about him" ---as it should be!
Self-confidence and self-sufficiency gives us the credit where it is not due. We trust our own actions and abilities rather than acknowledging God's power in our life. All things come from God! There is a healthy self-confidence that says, "God has made me and given me certain abilities. I will trust him to enable and empower me. I can do things because he is faithful to help me." Without God, we can do nothing. We are sufficient in him, where we "live, and move, and have our being."
Self-admiration, self-love---These focus our eyes on us rather than Christ. We do everything for the joy of our own reflection in the mirror rather than to reflect God's goodness to the world and bring glory to his name. All we do should glorify God.
Killing the self-sins is a difficult task. We must allow the Holy Spirit to build healthy character n us and produce good spiritual fruit. He will do this once we push out "self" and the fears and worries that accompany our self-focus. We will always fear and worry if we think everything depends on our own ability and work We only find peace in relying on God and resting in his love and promises.