But yet it is evident that religion consists so much in affection, as that without holy affection there is no true religion; and no light in the understanding is good which does not produce holy affection in the heart: no habit or principle in the heart is good which has no such exercise; and no external fruit is good which does not proceed from such exercises.
As it is with spiritual discoveries and affections given at first conversion, so it is in all subsequent illuminations and affections of that kind; they are all transforming. There is a like divine power and energy in them as in the first discoveries; they still reach the bottom of the heart, and affect and alter the very nature of the soul, in proportion to the degree in which they are given. And a transformation of nature is continued and carried on by them to the end of life, until it is brought to perfection in glory.
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.