Thomas Watson, The Art of Divine Contentment, p. 13:
Self-examination; for a man to take his heart, as a watch, all in pieces, to set up a spiritual inquisition, or court of conscience, and traverse things in his own soul; to take David's candle and lantern (Ps. 119.105) and search for sin; nay, as judge, to pass the sentence upon himself (2 Sam. 34.17) this is against nature, and will not easily be attained to without learning.
Thomas Watson, A Body of Practical Divinity, p. 371:
Thomas Watson, The Christian Soldier; or, Heaven Taken By Storm, p. 55-56:
Quest. 2. What is self-examination?
Ans. It is a setting up a court of conscience and keeping a register there, that by a strict scrutiny a man may see how matters stand between God and his soul. Self-examination is a spiritual inquisition, a heart-anatomy, whereby a man takes his heart, as a watch, all in pieces, and sees what is defective there. It is a dialogue with one's self, Ps. lxxvii.6, "I commune with my own heart." David called himself to account, and put interrogatories to his own heart. Self-examining is a critical descant or search; as the woman in the parable did light a candle, and search for her lost groat, Luke xv.8, so conscience is the candle of the Lord; search with this candle what thou canst find wrought by the Spirit in thee.
5. The fifth duty wherein we are to offer violence to ourselves, self-examination; a duty of great importance: it is a parleying with one's own heart, Psalm lxxxvii. 7. 'I commune with my own heart.' David did put interrogatories to himself. Self-examination is the setting up a court in conscience and keeping a register there, that by strict scrutiny a man may know how things stand between God and his own soul. Self-examination is a spiritual inquisition; a bringing one's self to trial. A good Christian doth as it were begin the day of Judgment here in his own soul. Self-searching is a heart-anatomy. As a Chirurgeon, when he makes a dissection in the body, discovers the intestina, the inward parts, the heart, liver, and arteries, so a Christian anatomizeth himself; he searcheth what is flesh and what is spirit; what is sin, and what is grace, Psalm lxxvii. 7. 'My spirit made diligent search:' As the woman in the Gospel did light a candle, and search for her lost groat, Luke xv. 8. so conscience 'is the candle of the Lord,' Prov. xx. 27. A Christian by the light of this candle must search his soul to see if he can find any grace there. The rule by which a Christian must try himself, is the Word of God. Fancy and opinion are false rules to go by. We must judge of our spiritual condition by the canon of Scripture. This David calls a 'lamp unto his feet,' Psalm cxix. 105. Let the word be the umpire to decide the controversy, whether we have grace or no. We judge of colours by the sun. So we must judge of the state of souls by the light of Scripture.
Self-examination is a great, incumbent duty; it requires self-excitation; it cannot possibly be done without offering violence to ourselves. 1. Because the duty of self-examination in itself is difficult: 1. It is actus reflexivus, a work of self-reflection; it lies most with the heart. 'Tis hard to look inward. External acts of religion are facile; to lift up the eye to Heaven, to bow the knee, to read a prayer; this requires no more labor than for a Catholic to tell over his beads; but to examine a man's self, to turn in upon his own soul, to take the heart as a watch all in pieces, and see what is defective; this is not easy. -- Reflective acts are hardest. The eye can see everything but itself. It is easy to spy the faults of others, but hard to find out our own.