Doctrinal and Practical Remarks on Psalm 143:1-12
1. Believers need no greater bulwark to their hope and confidence than can be found in the attributes of God, particularly his faithfulness and righteousness, as illustrated in providence and in the glorious plan of 
salvation, v. 1.
2. True piety rests not in forms of worship. Real prayer seeks and audience and an answer, vv. 1, 7.
3. Outward afflictions are often blessed to greatly quickening the conscience, and when they so act; they are to be esteemed among God’s precious gifts. No sooner is David in straits than he cries, “Enter not into judgment with thy servant,” v. 2.
4. True piety is profoundly humble, and deeply sensible of great unworthiness. It dares not rush thoughtlessly into the presence of God, nor challenge his examination, v. 2. Horne: “The thoughts of such a trial are enough to appal the soul of the best man living, to make his flesh tremble, and his bones shake, as if he stood at the foot of Sinai, and beheld Jehovah ready to break forth upon him in the flame of devouring fire.”
5. In true piety there is always a just and strong sense of accountability, v. 2. He who believes that he is not bound to obey God or humble himself under his mighty hand, nor plead for mercy, has not yet learned the first lessons of genuine godliness.
6. On whatever else regenerate men may differ, they all agree that they cannot stand before God on the ground of their own merits, v. 2. Compare Rom. 7:9. Luther: “I have tormented my body with fasting, watching, prayer, and other exercises, more than all who are now my enemies and persecutors; for I thought in this wise to satisfy the law, and shield my conscience from the rod of the oppressor. Yet it availed me naught; yea, the further I proceeded in this way, the more terrified I grew, so that I had nigh despaired, had not Christ mercifully looked upon me, and enlightened my heart by the light of his Gospel.” Several give us this story. I take it from Bultmann’s notes to Besser. Michael, an honest farmer, on his death bed called out to his son: “Jack, just reach down the Catechism from yonder shelf, to see how my past life agrees with it. Please, read me the commandments.” “Thou shalt have no other gods before me. Thou shalt not make to thyself any graven image, etc.” “O, these two have I always kept; I have neither worshipped idols, like the heathen, nor bowed down to images like the Roman Catholics. Please, proceed to the third.” “Thou shalt not take the name of the Lord thy God in vain,” etc. “Here I am right also; I never swore an oath except in a court of justice; pray, pass to the next.” “Remember the Sabbath-day to keep it holy.” “There I am not to blame either; I have always gone to church of a Sunday, and never played at cards, nor made my servants work. Which follows now?” “Honor thy father and mother,” etc. “Ay, as to that, Jack, I may well bid you follow my example; for when a boy I showed all honor and respect to my poor parents, God bless them! What is the next?” “Thou shalt not kill.” “Thank God, that is not on my conscience, I never slew a man not even in lawful war. Go on.” “Thou shalt not commit adultery.” “Of that I have kept clear also, and always been faithful to your poor mother. Proceed.” “Thou shalt not steal.” “I never took aught that did not belong to me. Next?” “Thou shalt not bear false witness against thy neighbour.” “I never swore falsely against any person. Are there any more?” “Yes, one: Thou shalt not covet.” “Stop, Jack! There, I must think a little; yes, I cannot say I have never coveted. Pray look for poor Mamma’s Bible on the subject.” And here Jack found a reference from Exodus 20 to Matthew 5 by which the farmer was soon led to see that he had broken the whole law; and, becoming fully conscious of his exceeding sinfulness, he betook himself to Christ and died a penitent.
7. Those who have never been persecuted may read such compositions as this Psalm with comparative indifference; but where the iron has entered the soul, such language as this of David is full of meaning, vv. 3, 4.
8. Henry: “It is sometimes the lot of the best men to have their spirits for a time almost overwhelmed, and their hearts desolate, and doubtless it is their infirmity. David was not only a great saint, but a great soldier, and yet even he was sometimes ready to faint in the day of adversity.” Yet thanks to the Holy One, who to the humble supplies supernatural courage, and thus brings them off conquerors.
9. Afflictions stir up a world of thought; sanctified afflictions, a world of useful thought, v. 5.
10. The language of Scripture in its strongest terms barely does justice to the subject, when it expresses the eager longings of the people of God for deliverance and salvation, v. 6. They have “groanings which cannot be uttered.”
11. In a sense the people of God live in a continual crisis, vv. 7, 8. Sometimes the urgency is greater than at others; but their warfare is never over till they rest in the bosom of the Redeemer. Now can any one tell what moment will bring still fiercer conflicts.
12. It is a dreadful thing to be in the power of the wicked, nor can our prayers for rescue from such dangers be too humble or too fervent, v. 9. God is sole and sufficient deliverer at such times. Blessed be his name, his ear is ever open to the cry of his people.
13. Whatever betides us, our great concern should be to know and do the will of God, v. 10. “To obey is better than sacrifice.”
14. But this cannot be done without the aid of the Holy Spirit, v. 10. He is the author of all saving views, right feelings and holy walking in the church of God.
15. If anything effectual is ever done by the Lord for our relief and salvation, all must come from his grace and mercy, v. 11. In the court of Heaven our names are worthless.
16. The case of the wicked is sad indeed. The very deliverance and salvation of God’s people and the mercies shown them require the utter destruction of the incorrigible, v. 12. Dickson: “Mercy to the Lord’s oppressed children, and justice against against their enemies, go together; and the work of justice on persecutors is a work of mercy to the oppressed.
Plumer, William S. Psalms, A Critical and Expository Commentary with Doctrinal and Practical Remarks, The Geneva Series of Commentaries (Carlisle: The Banner of Truth Trust, 1975), 1180-1181.