The heart, that was made according to God’s own heart, is now the reverse of it, a forge of evil imaginations, a sink of inordinate affections, and a storehouse of all impiety (Mark 7:21-22).
The mind is defiled; the thoughts of the heart are evil; the will and affections are defiled: the imagination of the thoughts of the heart, that is, whatsoever the heart frameth within itself by thinking, such as judgment, choice, purposes, devices, desires, every inward motion, or rather the frame of the thoughts of the heart, namely the frame, make, or mould of these is evil.
But is there not, at least, a mixture of good in them? No, they are only evil; there is nothing in them truly good and acceptable to God: nor can any thing be so, that comes out of that forge. Not one holy thought can ever be produced by the unholy heart.
O what a vile heart is this! O what a corrupt nature is this! The tree that always brings forth fruit, but never good fruit, whatever soil it be set in, whatever pains be taken with it, must naturally be an evil tree.
Surely that corruption is ingrained in our hearts, interwoven with our very natures, has sunk deep into our souls, and will never be cured but by a miracle of grace.
Adapted from The Whole Works of Thomas Boston, 8:27-28.