In making my way through "On Knowing Christ" by Jonathan Edwards, I have found one of the more explicit statements of Edwards' approach to the relation of head and heart in religious matters. Edwards is absolutely right that the head is first engaged to aprehend a truth about God and this is necessary. But then, the heart must be engaged to love that truth and move the affections. The rationalist approach to religion errs in making religion something merely of the mind. The enthusiast errs in believing religion can go directly to the heart without passing through the mind. Edwards stands in the middle and casts a pox on both their houses:
"THERE are two kinds of knowledge of divine truth, viz. speculative and practical, or in other terms, natural and spiritual. The former remains only in the head. No other faculty but the understanding is concerned in it. It consists in having a natural or rational knowledge of the things of religion, or such a knowledge as is to be obtained by the natural exercise of our own faculties, without any special illumination of the Spirit of God. The latter rests not entirely in the head, or in the speculative ideas of things; but the heart is concerned in it: it principally consists in the sense of the heart. The mere intellect, without the will or the inclination, is not the seat of it. And it may not only be called seeing, but feeling or tasting. Thus there is a difference between having a right speculative notion of the doctrines contained in the word of God, and having a due sense of them in the heart. In the former consists the speculative or natural knowledge, in the latter consists the spiritual or practical knowledge of them.
Neither of these is intended in the doctrine exclusively of the other: but it is intended that we should seek the former in order to the latter. The latter, or the spiritual and practical, is of the greatest importance; for a speculative without a spiritual knowledge, is to no purpose, but to make our condemnation the greater. Yet a speculative knowledge is also of infinite importance in this respect, that without it we can have no spiritual or practical knowledge."
-Jonathan Edwards in the sermon Christian Knowledge in "On Knowing Christ"