There are some brothers in Christ who are so focused on the local assembly of saints that they deny there is any congregation of a universal manner; that is, comprised of all the redeemed from every generation. This focus includes an emphasis on water baptism, to the exclusion of what John foretold - that One was coming who would baptism with fire and the Holy Spirit (Matt 3:11).
One passage that is said to be only about water baptism and the local fellowship is Ephesians 4, where we find this: Ephesians 4:4-5 (ESV) There is one body and one Spirit—just as you were called to the one hope that belongs to your call— one Lord, one faith, one baptism,
The context of this short passage should shed light on whether it is all and only about the local assembly and water baptism or if it's about something greater.
We know that Paul's letter to the saints at Ephesus was meant to be read to many local assemblies; it's a universal letter to the body of Christ. In the first three verses of chapter 3, Paul stresses identity in Christ and the unity of believers - dealing with one another in humility, gentleness, patience, and so on.
And then we find this: Ephesians 4:4-7 (ESV) There is one body and one Spirit—just as you were called to the one hope that belongs to your call— one Lord, one faith, one baptism, one God and Father of all, who is over all and through all and in all. But grace was given to each one of us according to the measure of Christ’s gift.
This letter reveals Paul's passion for all the saints to understand the unity we have because of our union with Christ Jesus, proclaiming there is one body, one Spirit, one hope, one Lord, one faith, one baptism, one God and Father of all. By this union with Christ we each have been given grace according to His gift.
Is there ANYTHING in this passage that hints Paul was addressing only the local assembly or numerous assemblies of saints? Is he not making much of the fact that ALL the saints share in these things, without regard to any temporal circumstances? One body, not numerous local bodies. One Spirit, not a separate Spirit for each locale. One hope, one Lord, one faith, one God and Father of ALL. This speaks to all saints in all locations and all generations. And one baptism.
Water baptism makes no one a child of God. The lack of water baptism keeps no one out of the kingdom of God.
But that baptism John mentioned, the baptism of the Holy Spirit and of fire, corresponds to the circumcision made without hands (Col 2:10-11). This baptism is what brings enemies of God into His kingdom as His friends and children; without this baptism, no one can enter into His domain.
As much as these brothers resist and insist, there is no argument that can be made from Ephesians 4 that restricts Paul's message of union and unity to the local assembly only. They can only make assertions in support of their view. Paul’s concern as an apostle was for the whole body of Christ, redeemed saints from every nation, tribe, and tongue. To deny this universal intent is to constrain the love of God for His people to clumps here and there, denying the communion we have through the Holy Spirit to all the saints.
It's too small a view of God's work and of His body.