In the Christian's lifelong battle against indwelling sin, his heart is the prize defended and assaulted. Proverbs 4:23 and John Owen agree when the former states, "Keep your heart with all vigilance, for from it flow the springs of life" and the latter, "Our hearts, as our Savior speaks, are our treasury. There we lay up whatsoever we have, good or bad; and thence do we draw it for our use." 
When the heart is filled up with good, the Law and the Gospel are its contents. But Owen makes the very important point that of the two, the Gospel is the superior antidote to temptation and its fruit, sin. He writes:
For the provision to be laid up it is that which is provided in the gospel for us. Gospel provisions will do this work; that is, keep the heart full of a sense of the love of God in Christ. This is the greatest preservative against the power of temptation in the world...Store the heart with a sense of the love of God in Christ, and his love in the shedding of it; get a relish of the privileges we have thereby—our adoption, justification, acceptance with God; fill the heart with thoughts of the beauty of his death—and you will, in an ordinary course of walking with God, have great peace and security as to the disturbance of temptations...A sense of his love and favor in Jesus Christ. Let this abide in you, and it shall garrison you against all assaults whatsoever...Contending to obtain and keep a sense of the love of God in Christ, in the nature of it, obviates all the workings and insinuations of temptation. 
He does not discount the utility of the Law, however:
A man may, nay, he ought to lay in provisions of the law also—fear of death, hell, punishment, with the terror of the Lord in them. But these are far more easily conquered than the other; nay, they will never stand alone against a vigorous assault. They are conquered in convinced persons every day; hearts stored with them will struggle for a while, but quickly give over. 
So it is the nature of the case that in dealing with sin and temptation, the Christian needs both the Law and the Gospel, with the Gospel as wielding greater efficacy. Churches who neglect one or the other, or both, benefit their members in no way.
Pastorally, however, a key application must not be missed. Pastors who emphasize the Law inordinately debilitate the sheep. Could it be that accountability of the members towards their elders is impaired by virtue of a fundamentalist, legalist bent in the latter? The erring member is predisposed to keeping quiet and left to dealing with his sin on his own because he foresees that acknowledging the error to his pastor would most likely result in humiliating condescension.
The gracious and Gospel-driven pastor would have the opposite outcome—members who are open to him and adequately mortifying sin in their lives.
1. Overcoming Sin & Temptation, eds. Kelly Kapic & Justin Taylor [Wheaton, Illinois: Crossway, 2006], 204.
2. Idid., 205.
3. Ibid., 204.