We can have fellowship with one another, if walk in the light  -  1 John 1:7

But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.

In this passage, John stated that an individual is either in the light or in darkness. If they are in the light, they are a member of the family of God, but if they were in darkness, they do not have anything in common with God, as there is not any darkness at all in God. Those who are in the light have fellowship with other believers and the blood of Christ cleanses them from all sin.