There are certain truths we accept as soon as we trust Christ; however, many of them must be made good in us through later experience. Every converted person, for example, is ready enough to acknowledge his own inherent badness, but it is only after long and fruitless struggles to be good that he is forced to the absolute conviction that "In me (that is, in my flesh) dwelleth no good thing" (Romans 7:18). It is not merely that I have sinned, but that I am in my old self nothing but sin: in me good is not.
Along with this goes the kindred truth that we are "without strength" (Romans 5:6), and perhaps this is even harder to learn. We freely confess to have no strength for salvation, but we think at first that we have (or ought to have) strength to perform that which is good, and to overcome the sin that dwells in us.
Eventually, it becomes evident that if fruit for God is to be brought forth in our lives, it must be through the new nature. So that these things do not remain as mere doctrines on the pages of our Bible, the Holy Spirit is given to the believer. This gift of the Holy Spirit is a wonderful thing! Life, peace, and freedom from the power of sin are all connected with Him (Romans 8:2-6).
We should never forget the constant need of prayer and meditation on God's Word. Although we have a new life and the indwelling Spirit, these things are never intended to weaken in our souls the sense of our absolute dependence upon God for strength for every moment. Prayer is the expression of dependence, and in the rich pastures of divine truth we shall find food in abundance.
—From Victory Over Sin by William Barker.