A large percentage of people believe it is impossible to be in a church that is not a
denomination. Some talk of an "invisible" church and the "visible" churches. Obviously,
they are claiming that the various denominations are the visible churches that are
ultimately united in the invisible church. I do not know of any passage of scripture
that even hints of an "invisible church." The undenominational church of the first
century was very visible. It was so visible that persecution was brought upon it (Acts
8:1-4). To speak of an "invisible church" is to indicate something intangible. But
the church of the first century was very tangible.
There are those who refer to the parable of the True Vine at John 15:1-8 as representing the different denominations being in fellowship with Christ. These people teach that the branches represent the different denominations. But examine the passage for yourself to learn what the individual branches represent. Each branch represents an individual disciple who must bear fruit to remain in spiritual union with Jesus Christ.
Many in the denominational world declare, "We are all going to heaven, but taking different roads to get there." Now, think about that for a moment, is that concept taught in the Bible? "Enter ye in at the strait gate: for wide is the gate, and broad is the way, that leadeth to destruction, and many there be which go in thereat: Because strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it" (Matthew 7:13-14). To claim that there is more than one way to heaven is to either suggest that the Bible itself teaches different ways or that it does not matter whether we adhere to what it teaches. Neither of these alternatives can be harmonized with the scriptures (Matthew 7:21-23; 1 Corinthians 1:10; Philippians 3:16; Ephesians 4:3-6).
Also, there are those who use the phrase, "other sheep I have which are not of this fold," recorded at John 10:16 to uphold religious division. They fail to stress the latter part of that verse, which states, "they shall hear my voice; and there shall be one fold, and one shepherd." All who hear Christís voice (the new covenant) shall become one fold, not many folds. When Gentiles (those of other races) obeyed the gospel of Christ and were added to the spiritual body of Christ (His church), they became one with Jewish Christians (Eph. 2:12-22).
Yes, undenominational Christianity is possible today when obedient believers submit to the one true standard, the Bible rather than the creeds and philosophies of fallible human beings (Philippians 3:16; Matthew 15:8-9; 1 Peter 4:11).