"If we confess our sins, He is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness" (I John 1:9).
It is easy to understand God's faithfulness regarding forgiveness. The Old Testament declares, "There is forgiveness with Thee," and "He delighteth in mercy" (Psalm 130:4; Micah 7:18). The New Testament confirms, proclaiming "His dear Son, in whom ye have redemption through His blood, even the forgiveness of sins" (Colossians 1:13-14). Our Lord promises to forgive, and He has made a way through His Son to do so. Thus, mercy bestowed reveals that His Word is true and His heart faithful, as we would expect.
God's justice in the matter of providing forgiveness, however, involves more consideration. How does justice fit into His pardon for our sins? The atoning work of the Lord Jesus Christ provides the answer.
"His blood is the propitiation not for our sins only, but for the sins of the whole world" (I John 2:2).
"This man, after He had offered one sacrifice for sins forever, sat down on the right hand of God" (Hebrews 10:12).
The Lord Jesus' redeeming actions on our behalf were so perfectly performed and completed that sin's death sentence has been served by the Lamb of God. Justice was done when the Father poured out His wrath on the Christ of Calvary, who was "made to be sin for us, who knew no sin, that we might be made the righteousness of God in Him" (II Corinthians 5:21). Forgiveness withheld from all who plead the merits of the Lord Jesus would therefore constitute an unrighteous act of double jeopardy on God' part. The punishment would not fit the crime because perfectly adequate punishment has already been suffered for the crime. Such injustice on God's part is impossible because "He is the Rock, His work is perfect: for all His ways are judgment: a God of truth and without iniquity, just and right is He" (Deuteronomy 32:4).
To "confess" our sins literally means that we "say the same thing" about them that God does ("homologeo" in the original language of Scripture). He says that His Son "offered one sacrifice for sins forever," and that "there remaineth no more sacrifice for sins" (Hebrews 10:26). We must say the same thing, first in the new birth that begins our eternal blessing of being "the vessels of mercy," and then in the ongoing maintenance of a clear conscience as we live our Christian lives (Romans 9:23; Hebrews 10:22). By His own determined standard of justice, God must forgive those who come to Him by the Blood-stained way of mercy He paved through His Son. Therefore, we plead both faithfulness and justice as we confess our sins in humble contrition, and as both we and the Father remember the perfectly atoning death sentence already served on the Son beloved of His heart, and of ours.
"Justice and judgment are the habitation of Thy throne: mercy and truth shall go before Thy face."