That which we have seen and heard we declare to you, that you also may have fellowship with us; and truly our fellowship is with the Father and with His Son Jesus Christ. …
But if we walk in the light as He is in the light, we have fellowship with one another, and the blood of Jesus Christ His Son cleanses us from all sin.
John’s purpose for writing this letter of 1 John is to help us have fellowship with the Church and especially with God. “Fellowship carries both the idea of a positive relationship that people share and participation in a common interest or goal” (Nelson's NKJV Study Bible note on 1 John 1:3).
Jesus Christ said, “I am the light of the world” ( John 8:12 ). We are to walk as children of light in “goodness, righteousness and truth” ( Ephesians 5:8-9 ), striving to avoid the works of darkness—sin. When we all strive to live and think like God, we can have real fellowship. Only Jesus Christ’s sacrifice can cleanse us from sin and allow us to have fellowship with the holy God.
For more about fellowship, see “Christian Fellowship.”