Tis a more glorious effect of power to make that holy that was so depraved and under dominion of sin, than to confirm holiness on that which before h… - Jonathan Edwards

From the blinding deceitful nature of sin. The heart of man is full of sin and corruption, and that corruption is of an exceedingly darkening, blinding nature. Sin always carries a degree of darkness with it; and the more it prevails, the more it darkens and deludes the mind. — It is from hence that the knowing whether there be any wicked way in us is a difficult thing. The difficulty is not at all for want of light without us, not at all because the word of God is not plain, or the rules not clear; but it is because of the darkness within us.

It does not answer the aim which God had in this institution, merely for men to have good commentaries and expositions on the Scripture, and other good books of divinity; because, although these may tend, as well as preaching, to give a good doctrinal or speculative understanding of the word of God, yet they have not an equal tendency to impress them on men's hearts and affections. God hath appointed a particular and lively application of his word, in the preaching of it, as a fit means to affect sinners with the importance of religion, their own misery, the necessity of a remedy, and the glory and sufficiency of a remedy provided; to stir up the pure minds of the saints, quicken their affections by often bringing the great things of religion in their remembrance, and setting them in their proper colours, though they know them, and have been fully instructed in them already.

Since holiness is the main thing that excites, draws, and governs all gracious affections, it is no wonder that all such affections tend to holiness. That which men love, they desire to have and to be united to, and possessed of. That beauty which men delight in, they desire to be adorned with. Those acts which men delight in, they necessarily incline to do.