"It is with indwelling sin as with a river. While the springs and fountains of it are open, and waters are continually supplied unto its streams, set a dam before it, and it causes it to rise and swell until it bear down all or overflow the banks of it. Let these waters be abated, dried up in some good measure in the springs of them, and the remainder may be coerced and restrained. But still, as long as there is any running water, it will constantly press upon what stands before it, according to its weight and strength, because it is its nature to do so; and if by any means it [would] make a passage, it will proceed.
So it is with indwelling sin: while the springs and fountains of it are open, in vain is it for men to set a dam before it by their convictions, resolutions, vows, and promises. They may check it for a while, but it will increase, rise high, and rage, at one time or another, until it bears down all those convictions and resolutions, or makes itself an under-ground passsage by some secret lust, that shall give a full vent unto it.
But now, suppose that the springs of it are dried up by regenerating grace, the streams or actions of it will be abated by holiness, yet while anything remains of it, it will be pressing constantly to have vent, to press forward into actual sin; and this is its lusting." (John Owen, Overcoming Sin and Temptation, p. 272)
1. Sin is an internal problem, not an external problem. Sin dwells in the heart.
2. The impulse of indwelling sin is always to sin. Indwelling sin inclines the heart to evil. As waters in a river will flow as far as possible, so sin will incline the heart to as much evil as possible.
3. External barriers to sin may hinder sinful actions, but they are insufficient to deal with sinful motives and desires. A river is going to press against a dam with all of its weight and strength, and if possible, will break through or find some other outlet. Indwelling sin like a river will press against our vows and resolutions and will find an outlet, notwithstanding our attempts to stop it.
4. The only real solution to indwelling sin is "dry up" the "springs" of it. Only regenerating grace (new birth) can accomplish this. We need the power of the Holy Spirit to transform us deeply. When the Spirit deals with our hearts, motives and desires are changed - not just actions.
5. However, even in believers, whatever remains of indwelling sin will continually seek to find an outlet. This accounts for the continual need for watching lest we fall into temptation and for putting sin to death.