Paul explained in his letter to the Romans that righteousness is something that is obtained through faith in Jesus Christ (Romans 3:22). Paul said, “For there is no distinction: for all have sinned and fall short of the glory of God, and are justified by grace as a gift, through the redemption that is in Christ Jesus, whom God put forward as a propitiation by his blood, to be received by faith” (Romans 3:22-25).  The Greek word that is translated propitiation, hilasterion (hil-as-tayˊ-ree-on) refers to the mercy seat that covered the Ark of the Covenant where the tablets with the Ten Commandments written on them were kept (Exodus 25:17-21). God told Moses about the mercy seat, “There I will meet with you, and from above the mercy seat, from between the two cherubim that are on the ark of the testimony, I will speak with you about all that I will give you in commandment for the people” (Exodus 25:22). Hilasterion in Romans 3:25 refers to the “propitiator, one who makes propitiation” (G2435). The propitiator is the one “to atone for (sin)” (G2433); and in so doing, Jesus provided the means for reconciliation between God and all who have sinned.

The Apostle John explained in his first letter that we must first confess our sin in order for God to forgive us. John said, “If we say we have no sin we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness” (1 John 1:8-9). “To ‘confess’ (homologeo [G3670]) means to agree with God that sin has been committed. Even though Christ’s death satisfied God’s wrath toward the believer’s sin (1 John 2:1, 2), the inclination to sin still remains within man (vv. 8, 10). Therefore he must realize the need to continue in a right relationship with God by confession of sin. God grants forgiveness in accordance with his ‘faithful and just’ nature” (note on 1 John 1:9). An example of confession and forgiveness of sin can be found in the life of King David. It says in 2 Samuel 12:1-13:

And the Lord sent Nathan to David. He came to him and said to him, “There were two men in a certain city, the one rich and the other poor. The rich man had very many flocks and herds, but the poor man had nothing but one little ewe lamb, which he had bought. And he brought it up, and it grew up with him and with his children. It used to eat of his morsel and drink from his cup and lie in his arms, and it was like a daughter to him. Now there came a traveler to the rich man, and he was unwilling to take one of his own flock or herd to prepare for the guest who had come to him, but he took the poor man’s lamb and prepared it for the man who had come to him.” Then David’s anger was greatly kindled against the man, and he said to Nathan, “As the Lord lives, the man who has done this deserves to die, and he shall restore the lamb fourfold, because he did this thing, and because he had no pity.”

Nathan said to David, “You are the man! Thus says the Lord, the God of Israel, ‘I anointed you king over Israel, and I delivered you out of the hand of Saul. And I gave you your master’s house and your master’s wives into your arms and gave you the house of Israel and of Judah. And if this were too little, I would add to you as much more. Why have you despised the word of the Lord, to do what is evil in his sight? You have struck down Uriah the Hittite with the sword and have taken his wife to be your wife and have killed him with the sword of the Ammonites. Now therefore the sword shall never depart from your house, because you have despised me and have taken the wife of Uriah the Hittite to be your wife.’ Thus says the Lord, ‘Behold, I will raise up evil against you out of your own house. And I will take your wives before your eyes and give them to your neighbor, and he shall lie with your wives in the sight of this sun. For you did it secretly, but I will do this thing before all Israel and before the sun.’” David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die.”

“Nathan used his parable (2 Samuel 12:1-4) to skillfully bring David to condemn himself, and David painfully realized the consequences of his sin. He had violated four of the ten commandments in one rash sin: you shall not commit murder, you shall not steal, you shall not commit adultery, and you shall not covet your neighbor’s wife. Although it was about a year later, David sincerely repented of his sin (cf. Psalm 32:5; 51:1-19). While his repentance brought about forgiveness from God, it did not prevent him from suffering the consequences of his sin. God revealed that because of David’s sin, the son born from his adulterous relationship would die (vv. 14, 18), the sword would never depart from his house (v. 10), evil would come upon him from his own family (v. 11; see chapters 15-18), and his wives would be publicly shamed (v. 11, cf. 2 Samuel 16:22). While true repentance does bring forgiveness from God, it does not necessarily eliminate the consequences of sin” (note on 2 Samuel 12:1-14).

David talked about confession of sin in Psalm 32. David described in detail for us the emotional experience he went through and the relief he felt after Nathan confronted him with his sinful behavior. David wrote:

For when I kept silent, my bones wasted away
    through my groaning all day long.
For day and night your hand was heavy upon me;
    my strength was dried up as by the heat of summer. Selah

I acknowledged my sin to you,
    and I did not cover my iniquity;
I said, “I will confess my transgressions to the Lord,”
    and you forgave the iniquity of my sin. Selah (Psalm 32:3-5)

David used the Hebrew word yadah (yaw-dawˊ) to describe his act of confession. The essential meaning of yadah “is an act of acknowledging what is right about God in praise and thanksgiving (1 Chronicles 16:34). It can also mean a right acknowledgment of self before God in confessing sin (Leviticus 26:40) or of others in their God-given positions (Genesis 49:8)…This rightful, heavenward acknowledgment is structured in corporate worship (Psalm 100:4; 107:1, 8, 15, 21, 31), yet is also part of personal lament and deliverance (Psalm 88:11 [10]).

In Ezra 10:1-17, the returned exiles who had married foreigners confess their sin and vowed to separate themselves from their foreign wives. It says in Ezra 10:1-3, “While Ezra prayed and made confession, weeping and casting himself down before the house of God, a very great assembly of men, women, and children, gathered to him out of Israel, for the people wept bitterly. And Shecaniah the son of Jehiel, of the sons of Elam, addressed Ezra: ‘We have broken faith with our God and have married foreign women from the people of the land, but even now there is hope for Israel in spite of this. Therefore, let us make a covenant with our God to put away all these wives and their children, according to the counsel of my lord and of those who tremble at the commandment of our God, and let it be done according to the Law.” Shecaniah said the people had broken faith with God, meaning they had willfully disobeyed him (H4603).

Faithlessness or being unfaithful to God was the primary reason the people of Israel did not experience God’s rest after they entered the Promised Land, and because of it, God allowed them to be taken into captivity. It says in Hebrews 3:19, “So we see that they were unable to enter because of unbelief.” Jesus rebuked his disciples on more than one occasion because of their unbelief. When his disciples were unable to cast a demon out of a man’s son, Jesus asked, “O faithless and twisted generation, how long am I to be with you? How long am I to bear with you?” (Matthew 17:17). Afterward, the disciples asked Jesus privately, “Why could we not cast it out?” (Matthew 17:19). Jesus’ reply, “Because of your unbelief; for assuredly, I say to you, if you have faith as a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move; and nothing will be impossible for you” (Matthew 17:20, NKJV), indicated that our reliance upon God is measured and validated by the supernatural manifestation of his power in our lives.

Paul confessed to Timothy that he was acting in unbelief when he persecuted the church before he was converted on the road to Damascus. Paul said, “I thank him who has given me strength, Christ Jesus our Lord, because he judged me faithful, appointing me to his service, though formerly I was a blasphemer, persecutor, and insolent opponent. But I received mercy because I had acted ignorantly in unbelief” (1 Timothy 1:12-13). Paul compared his former life as a blasphemer, persecutor, and insolent opponent of Christ to his current state of being judged faithful to serve in Jesus’ ministry. Paul attributed his transformed life to “the grace of our Lord” which “overflowed for me with the faith and love that are in Christ Jesus” (1 Timothy 1:14). Paul went on to say, “The saying is trustworthy and deserving of full acceptance that Christ Jesus came into the world to save sinners of whom I am the foremost” (1 Timothy 1:15). Paul wanted Timothy, and everyone else to know, that he was a prime example of how confession of sin transforms your life. Paul explained that the reason God forgives sinners is so that he “might display his perfect patience as an example to those who were to believe in him for eternal life” (1 Timothy 1:16); and then, Paul concluded his topic of God saving sinners with a tribute to his Savior, “To the King of the ages, immortal, invisible, the only God, be honor and glory forever and ever. Amen.”