One of the challenges of Christian life is that there is a very high and specific standard set for a believer in God. Such a believer is called on to take on the attitudes of God himself. Inevitably people with even the highest of intentions find themselves not managing to achieve what they feel they should be doing. Then they wonder why it is that they always seem to fail.
A Divided Self
There is nothing new about this situation. It was expressed by one of the great early Christians, Paul. In Romans 7, he wrote on this very issue,
Romans 7:15: For I don't know what I am doing. For I don't practice what I desire to do; but what I hate, that I do. 16 But if what I don't desire, that I do, I consent to the law that it is good. 17 So now it is no more I that do it, but sin which dwells in me. WEB
The greater context of the chapter is about living a life that is consistent with the Christian values that he knew. In particular, that section shows how a Christian life means taking on a new identity in Christ with new values and direction. Paul makes the observation that it is all to easy to slip back into the old “self”, even with the best of intentions to change.
In this way, a person can feel divided, and begin to see part of themself as foreign. There is an aspect of their human nature that feels like an adversary to their rational thought. This is a natural feeling for a person in this position, as expressed by Paul in Romans.
Satan: Adversary Unnamed
In this context, it is natural to think of the idea of “satan”. This is a Hebrew word that appears in the Bible untranslated. It is used as a name to refer to an opponent or adversary, and appears in the Bible as something of a “John Doe” of evil. Jesus calls the enthusiastic apostle Peter by this name when he was tempting Jesus to follow normal human emotions,
Matthew 16:21: From that time, Jesus began to show his disciples that he must go to Jerusalem and suffer many things from the elders, chief priests, and scribes, and be killed, and the third day be raised up. 22 Peter took him aside, and began to rebuke him, saying, "Far be it from you, Lord! This will never be done to you." 23 But he turned, and said to Peter, "Get behind me, Satan! You are a stumbling-block to me, for you are not setting your mind on the things of God, but on the things of men." WEB
Peter would look back on this as a moment when he let himself be ruled by that nature he wanted to avoid.
It comes as both a consolation and a warning. It is a consolation in that even the greatest of followers of Jesus succumbed to it, but a warning for precisely the same reason.
Living a Christian life is something of a challenge because it is a conscious effort to break away from the common human nature of pride and self-preservation.
Some people will present the idea of evil being something that comes from outside a person - from an external entity, and so promote building a defensive shell about yourself, but this doesn't help, because instead it is something that comes from the nature inside. The epistle of James demonstrates this,
James 1:13: Let no man say when he is tempted, "I am tempted by God," for God can't be tempted by evil, and he himself tempts no one. 14 But each one is tempted, when he is drawn away by his own lust, and enticed. 15 Then the lust, when it has conceived, bears sin; and the sin, when it is full grown, brings forth death. WEB
So a Christian life is not one that is about standing up and defending oneself from the evil of the world, but rather one that is willing to rebuild self and, losing personal identity, to instead take on the attitudes and life expressed in Christ.