We must not love God only with the heart, but with the whole heart. Pray mark this: perfect hatred and perfect love know no such thing as the world calls prudence. If you perfectly hate any one, all things about him displease you; whatever he says or does, though it be never so good, it seems to you to be evil: so if you perfectly love any one, all things about him please you. Some expound this totality by this distinction: We are to love God with the whole heart positively and negatively: positively, where all powers of the will are set to love God; and this we cannot perfectly do while we are travellers, till we come to our heavenly country: but, negatively, thou shalt so love God, that nothing contrary to the love of God shall be entertained in thy heart; and this we may attain to a pretty tolerable perfection of in this life.
The whole heart is opposed either to a divided and dispersed heart, or to a remiss and a sluggish heart: God doth as much abominate a partnership in our love, as a husband or wife abhors any such thing in their conjugal relation. We must love nothing but God, or that which may please God. He that loves God with his heart, and not with his whole heart, loves something else, and not God.
As the whole heart is opposed to a remiss and sluggish heart, the meaning is this,—the care of our heart should be set upon nothing so much as upon the loving and pleasing of God; we must prefer God alone before all other objects of our love, and there must be an ardency of affection: whatever we do, it must be for his sake, and according to his will. - Samuel Annesley (1620-1696)
Puritan Sermons, Volume 1 (Wheaton, IL: Richard Owen Roberts, Publishers, 1981), 576-77.