Sin & Temptation

The fundamental problem is unbelief in the gospel. At the root...of all Christian failures to live right - i.e. not give their money generously, not tell the truth, not care for the poor, not handle worry and anxiety - is the sin under all sins, the sin of unbelief, of not rejoicing deeply in God's grace in Christ, not living out of our new identity in Christ. This means that every week in a different way the minister must apply the gospel of salvation by grace through faith through Christ's work.
Tim Keller from "Preaching in a Post-modern City"

Bound as I was, not with another's irons, but by my own iron will. My will the enemy held, and thence had made a chain for me, and bound me. For of a forward will, was a lust made; and a lust served, became custom; and custom not resisted, became necessity. By which links, as it were, joined together (whence I called it a chain) a hard bondage held me enthralled. But that new will which had begun to be in me, freely to serve Thee, and to wish to enjoy Thee, O God, the only assured pleasantness, was not yet able to overcome my former wilfulness, strengthened by age. Thus did my two wills, one new, and the other old, one carnal, the other spiritual, struggle within me; and by their discord, undid my soul.
Saint Augustine Confessions (8.10)

If you are a preacher of Grace, then preach a true, not a fictitious grace; if grace is true, then you must bear a true and not a fictitious sin. God does not save people who are only fictitious [or imaginary] sinners. Be a sinner and let your sins be strong [sin boldly], but believe and rejoice in Christ even more boldly still. For he is the victor over sin, death, and the world.
Martin Luther