1 John 1:6-7 If we say that we have fellowship with Him, and walk in darkness, we lie and do not practice the truth. 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.

This will sound judgmental, but there are those individuals that claim to know Jesus as Savior but never go to church, haven’t quit handshaking with the world, still cuss, still drink and get buzzed, only pray or ask for prayer when somethings wrong, and only read the Bible when they do go to a church service.
Yet, they maintain they are living for the Lord.
John says, they “do not practice the truth!”
Notice the second verse says that when we walk in the light, like Jesus, we have fellowship with one another.
The word for fellowship is the same word often used for communion. It indirectly indicates a gathering, as in a church gathering.
One of the main lessons the Bible teaches, especially those of Jesus, is the relationship you have with God and then with others.
The Law and the Prophets are based on relationships.
As Jesus said, “Love (relationship) the Lord your God with all your heart, mind, soul, and strength. And love (relationship) your neighbor as yourself.”
For someone to fellowship with those that do not encourage a better relationship with the Lord is to fellowship with darkness.
Paul said, “Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness? And what accord has Christ with Belial? Or what part has a believer with an unbeliever? And what agreement has the temple of God with idols?” 2 Cor 6:14-16
Christians need the fellowship of Christians – as iron sharpens iron.
Christians need to present the Gospel to unbelievers but must live separately (sanctified) from them.