Thomas Chalmers (1780–1847), a well-known Scottish preacher, in his famous sermon “The Expulsive Power of a New Affection,” says it well: 

Seldom do any of our habits or flaws disappear by a process of extinction through reasoning or “by the mere force of mental determination.” Reason and willpower are not enough. “But what cannot be destroyed may be dispossessed…The only way to dispossess [the heart] of an old affection is by the expulsive power of a new one.” 

A young man, for example, may “cease to idolize pleasure, but it is only because the idol of wealth has become the stronger and gotten the ascendancy” and is enabling him to discipline himself for prosperous business. “Even the love of money ceases to have the mastery over the heart” if it’s drawn into another world of ideology and politics, “and he is now lorded over by the love of power.” 

But “there is not one of these [identity] transformations in which the heart is left without an object. Its desire for one particular object may be conquered, but… its desire for having some one object” of absolute love “is unconquerable.” It is only when admitted “into the number of God’s children through the faith that is in Jesus Christ [that] the spirit of adoption is poured out upon us. It is then that the heart, brought under the mastery of one great and predominate affection, is delivered from the tyranny of its former desires, in the only way that deliverance is possible.” So it isn’t enough to hold out a “mirror of its imperfections” to your soul. It’s not enough to lecture your conscience. Rather, you must “try every legitimate method of finding access to your hearts for the love of him who is greater than the world.