If all Christians believe and accept the same truth, why are there various denominations?
There is a very good and important reason why we now have so many different Christian denominations. Up until the early sixteenth century the Roman Catholic Church dominated the spiritual life of Europe. Then Martin Luther and his allies in the Protestant Reformation broke away from Catholicism. They translated the Bible into the language of the people. They made the case that every believer has the right to read the Scriptures for himself or herself. The result was a veritable explosion of new ideas and conflicting opinions about the interpretation of various biblical passages.
These disagreements, in turn, led to the formation of a number of different Christian fellowship groups. Each group was made up of a collection of people who more or less agreed on what they considered the major points of the faith. We are the heirs of this fertile fragmentation of Catholic Christendom.
There are both positive and negative aspects to the situation as it exists today. It’s bad because Jesus indicated very clearly that He wanted His followers to be one (John 17:23). But it’s also good because it fosters honest discussion and open dialogue about the deeper meaning of the Bible and the best way to live the Christian life. And when it comes to something as important as understanding God’s Word, two heads are always better than one. As Scripture says, “In the multitude of counselors there is safety” (Proverbs 11:14).
Here’s the crucial question: in the final analysis, exactly how different are the various Christian denominations? Do their respective teachings really represent conflicting “concepts of God,” or are they just variations on a grand theme? We’d suggest that the second option is closer to the truth.
We agree with author C. S. Lewis that there is such a thing as “Mere Christianity.” As we see it, there is an essential core of Bible-based beliefs shared by all Christian denominations. The vast majority of believers affirm such basic truths as the love of God, the reality of sin, the need for atonement, the deity of Jesus Christ, the efficacy of His death on the cross, the historicity of His resurrection, the indwelling power of the Holy Spirit, and the necessity of faith. To the extent that Christians from different church backgrounds can find common ground in this body of shared doctrine, we think it’s fair to say that they are “one in Christ.” This is true in spite of the denominational distinctions that divide them on the organizational level.
[excerpted/edited from source]
[Editorial note: the #1 essential core belief is the inerrancy of Scripture. All doctrine must be proved by the word of God which clearly testifies to the 5 “Solas” of the Reformation and the T U L I P acronym. (see below)]