John Flavel (Works, vol. 5, p. 588):
O professor, if thy condition be good, thy heart right, thou wilt desire to know the very worst of thyself; and when thou hast made the deepest search, thou canst, thou wilt still fear thou hast not been severe enough, and impartial enough to thyself; nothing will give thee more content than when thou feelest the word dividing thy soul and spirit, thy joints and marrrow; nothing so much comforts thee under, or after an affliction, as the discovery it hath made of my heart; thou wilt seem to feel with what affection those words came from the prophet’s lips, Jer. 12:2. “But thou, O Lord, knowest me, thou hast seen me, and tried my heart towards thee.” O what a refreshing sweetness will stream through thy heart, and all the powers of thy soul, when thou canst make the like appeal to God with like sincerity! And certainly, without such a disposition of spirit towards the trial of our graces, we can have little evidence of the truth of them.