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. Fellowship is based on your walking in what you know. When a person walks behind light, he cannot have fellowship with the saints. The reason is that he does not have fellowship with God. If one does not have fellowship with God, he cannot have fellowship with the saints of God.
Truth is the creator of fellowship.
If men and women are walking in the light, fellowship is automatic. If you are allowing Christ to work in your life as you ought to be, you will be closer to God and closer to the saints of God. Light helps you to discriminate between that which pleases God and that which does not please Him. Light will expose that which is evil, and it will reveal secrets. Also, it uncovers darkness.