This is one of the more abused passages, wherein people attempt to shed their responsibility, by blaming something or someone else for their own wrongdoing.
In Romans 8 and 1 Corinthians 3, we are likewise told that the spirit of God dwells in the Christian, which is in contrast to the statement here where sin is said to indwell the Christian.
What determines which one is in control, comes from your decisions. Therefore, it is the individual who is always responsible and held accountable for their own thoughts and actions.
Therefore, every Christian can say that he does not choose to do evil or bad things, but would prefer to do good things, however it is the sin nature and its strong influence, which leads him astray.
This fundamental truth of human nature, should end the argument as to whether man is naturally good or naturally bad.
And the answer is, that the inherent nature of man is to be bad and corrupt, because of the sin nature which indwells within him. But man also has volition, where he has the ability to make decisions for good or for bad.
Without truth or Bible doctrine within his soul, then the individual is at a disadvantage and is in effect a slave to the sin nature.
With Bible doctrine within the soul, if a person has in fact taken the time to learn Bible doctrine, then the individual is at an advantage over the sin nature, and has a much better ability to choose for good.
Study [by instruction],
to show thyself approved [spiritually mature]
a workman [student]
that need not be ashamed [ignorant],
rightly dividing [learning, understanding, discerning]
the word of truth [Bible doctrine].