is the confession of sin, according to Thomas Watson:
Let us show ourselves penitents by sincere confession of sin. The thief on the cross made a confession of his sin: `we indeed are condemned justly' (Luke 23.41). And Christ said to him, `Today shalt thou be with me in paradise' (Luke 23.43), which might have occasioned that speech of Augustine's, that confession of sin shuts the mouth of hell and opens the gate of paradise. That we may make a free and ingenuous confession of sin, let us consider:
(1) Holy confession gives glory to God: `My son, give, I pray thee, glory to the Lord God of Israel, and make confession unto him' (Josh. 7.19). A humble confession exalts God. What a glory is it to him that out of our own mouths he does not condemn us? While we confess sin, God's patience is magnified in sparing, and his free grace in saving such sinners.
(2) Confession is a means to humble the soul. He who subscribes himself a hell-deserving sinner will have little heart to be proud. Like the violet, he will hang down his head in humility. A true penitent confesses that he mingles sin with all he does, and therefore has nothing to boast of. Uzziah, though a king, yet had a leprosy in his forehead; he had enough to abase him (2 Chron. 26.19). So a child of God, even when he does good, yet acknowledges much evil to be in that good. This lays all his feathers of pride in the dust.The Doctrine of Repentance, 1668, (Carlisle, PA: Banner of Truth Trust, 2009)
(3) Confession gives vent to a troubled heart. When guilt lies boiling in the conscience, confession gives ease. It is like the lancing of an abscess which gives ease to the patient.
(4) Confession purges out sin. Augustine called it `the expeller of vice'. Sin is a bad blood; confession is like the opening of a vein to let it out. Confession is like the dung-gate, through which all the filth of the city was carried forth (Neh. 3.13). Confession is like pumping at the leak; it lets out that sin which would otherwise drown. Confession is the sponge that wipes the spots from off the soul.
(5) Confession of sin endears Christ to the soul. If I say I am a sinner, how precious will Christ's blood be to me! After Paul has confessed a body of sin, he breaks forth into a gratulatory triumph for Christ: `I thank God through Jesus Christ' (Rom. 7.25). If a debtor confesses a judgment but the creditor will not exact the debt, instead appointing his own son to pay it, will not the debtor be very thankful? So when we confess the debt, and that even though we should for ever lie in hell we cannot pay it, but that God should appoint his own Son to lay down his blood for the payment of our debt, how is free grace magnified and Jesus Christ eternally loved and admired!
(6) Confession of sin makes way for pardon. No sooner did the prodigal come with a confession in his mouth, `I have sinned against heaven', than his father's heart did melt towards him, and he kissed him (Luke 15.20). When David said, `I have sinned', the prophet brought him a box with a pardon, `The Lord hath put away thy sin' (2 Sam. 12.13). He who sincerely confesses sin has God's bond for a pardon: `If we confess our sins, he is faithful and just to forgive us our sins' (1 John 1.9). Why does not the apostle say that if we confess he is merciful to forgive our sins? No; he is just, because he has bound himself by promise to forgive such. God's truth and justice are engaged for the pardoning of that man who confesses sin and comes with a penitent heart by faith in Christ.
(7) How reasonable and easy is this command that we should confess sin! (a) It is a reasonable command, for if one has wronged another, what is more rational than to confess he has wronged him? We, having wronged God by sin, how equal and consonant to reason is it that we should confess the offence. (b) It is an easy command. What a vast difference is there between the first covenant and the second! In the first covenant it was, if you commit sin you die; in the second covenant it is, if you confess sin you shall have mercy. In the first covenant no surety was allowed; under the covenant of grace, if we do but confess the debt, Christ will be our surety. What way could be thought of as more ready and facile for the salvation of man than a humble confession? `Only acknowledge thine iniquity' ( Jer. 3.13). God says to us, I do not ask for sacrifices of rams to expiate your guilt; I do not bid you part with the fruit of your body for the sin of your soul, `only acknowledge thine iniquity'; do but draw up an indictment against yourself and plead guilty, and you shall be sure of mercy.
All this should render this duty amiable. Throw out the poison of sin by confession, and `this day is salvation come to thy house'.