1Cor 1:9 God is faithful, by whom you were called into the fellowship of his Son, Jesus Christ our Lord.
1. We are called into fellowship in Christ (His body) by the Father. This is not an invitation to come join a church or any organization. As with all gifts and callings of God, only God's sovereign election applies, i.e. it is a permanent and irrevocable calling.. If he elects you to membership, you are a member whether you seek to gather with others or not. Romans 8:28-39; Romans 11:29; 1 Cor 12:12-18
1 That which was from the beginning, which we have heard, which we have seen with our eyes, which we looked upon and have touched with our hands, concerning the word of life--
2 the life was made manifest, and we have seen it, and testify to it and proclaim to you the eternal life, which was with the Father and was made manifest to us--
3 that which we have seen and heard we proclaim also to you, so that you too may have fellowship with us; and indeed our fellowship is with the Father and with his Son Jesus Christ.
4 And we are writing these things so that our joy may be complete.
5 This is the message we have heard from him and proclaim to you, that God is light, and in him is no darkness at all.
6 If we say we have fellowship with him while we walk in darkness, we lie and do not practice the truth.
7 But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin.
2. God's call to fellowship is established in the accurate and true proclaiming of the Gospel and teaching of his Word. God is light and His Word is light.If we walk in the light that He is, (all else is darkness0 we have fellowship with Him and with one another; the blessing and fruit being forgiveness for all our sins, past, present, and future.
2Cor 13:14 The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all.
3. Paul is in perfect agreement with John. Fellowship is the calling that reveals God's love; by the sufficiency of His grace, made effectual in and through His Son, and made actual in us by the power of the Holy Spirit. 1John 4:4-16; 1John 2:19
24 And let us consider how to stir up one another to love and good works,
25 not neglecting to meet together, as is the habit of some, but encouraging one another, and all the more as you see the Day drawing near.
42 And they devoted themselves to the apostles' teaching and the fellowship, to the breaking of bread and the prayers.
43 And awe came upon every soul, and many wonders and signs were being done through the apostles.
44 And all who believed were together and had all things in common.
45 And they were selling their possessions and belongings and distributing the proceeds to all, as any had need.
46 And day by day, attending the temple together and breaking bread in their homes, they received their food with glad and generous hearts,
47 praising God and having favor with all the people. And the Lord added to their number day by day those who were being saved.
4. We are told not to forsake gathering together. From the first century church to this day there are those who choose not to meet with any of the saints. Of course true fellowship, as previously demonstrated here, is found only in the accurate and true teaching of Christ and His Word.
Therefore, attending a service in a building, consisting of pew and "altar", listening to the "degreed man of God" preach, meeting only on the seventh day, or the sixth day, or Wednesday etc. etc. cannot be defined as true fellowship.
Staying home and watching christian television and/or listening to Christian radio is not fellowship. The church is derelict in its; duty when the saints neglect to visit the elderly and the sick.
Fellowship, as with all callings of God, is a daily walk.
22 But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, and to innumerable angels in festal gathering,
23 and to the assembly of the firstborn who are enrolled in heaven, and to God, the judge of all, and to the spirits of the righteous made perfect,
Soli Deo Gloria