What does 1 John 1:9 mean?

In this fourth "if" statement, John refers to confession of our sins to God. The pattern of positive / negative statements once again sets up the reader to expect a positive "if" statement in this phrase (see notes in 1 John 1:8). Confession of sins has always been seen as a godly practice among those who turn to the Lord (Leviticus 5:5; 16:21; Numbers 5:7; Ezra 10:1) and has been seen as a source of healing (James 5:16).

Those who confess sins are reassured that God will forgive, and remove that sin's impact on fellowship. Note that even though this passage is written to believers, John states that those who confess sins are both forgiven and cleansed. Though believers are forgiven at the point of salvation, there is also an ongoing sense in which believers need to confess sin and experience forgiveness and cleansing. Cleansing was an important part of the Mosaic Law, mentioned some 14 times in the book of Leviticus alone. It was the goal of those who brought a sacrifice to the Lord in the tabernacle and temple.

When we have an argument with others, it creates a barrier to fellowship. Since a barrier between us and God will always be our fault, our need for confession is important for our relationship to God.