Paul says something fascinating: "We should all say the same thing" (I Cor 1:10). This does not jive with today's different denominations of Christianity. They do not help define what is a Christian. They don't define what is Christian living because they all define it differently.
We have so many different denominations of Christianity today, with so many different voices saying so many different things, it's easy to be confused. It's like they don't define things - but just disagree on things. If you look in the Yellow Pages of the telephone book under 'churches,' it can cause spiritual insanity. I often refer to all of this as "The Second Tower of Babel."
WHAT IS THE DEFINITION OF TRUTH?
The book of John defines truth as a person. Jesus says, "I am the way, the truth and the life" (John 14:6). Jesus says the reason he came was to bear witness, or give testimony to the truth (John 18:37). Truth only comes from God.
We humans invent different theories, opinions and beliefs. But they are not truth, according to the Bible, unless they are in line with what God says in his New Testament gospel of truth. Paul says we should only preach the New Testament (II Cor 3:6), because this is where Bible truth culminates. It is the gospel that fulfills the word of God in our lives (Col 1:23-25).
FAITH IN JESUS IS LIVING IN TRUTH
It's interesting that more than one verse in the New Testament distinguishes between what are called (1) saints (or born again Christians), and (2) those who are faithful to Jesus. Ephesians 1:1 does this, at least in the King James Version (some more modern versions change many things, including this verse). It's like the Bible doesn't include everyone who believes as being faithful in Christ.
Thus all the different denominations of Christianity: all defining what Christian beliefs really are, and what is Christian living. They are all over the board on the definition of truth, living in truth, and faith in Jesus. That's why so many people 'church shop' until the find one that 'tickles their ears,' as Paul says, and says what they want to hear - often having no bearing on truth.
WHO IS JESUS TO YOU?
In II Timothy 2:2, Paul says to only commit the truth to FAITHFUL men, not to all Christian pastors and preachers. Paul makes a big distinction between 'fathers of the gospel' vs. 'instructors in Christ' (I Cor 4:15).
In the first 15 verses of Ephesians 1, Paul commends them for their faith and love. He says they know their adoption, and God's choosing of them, they know their redemption by Christ's blood, and they are included in 'the dispensation of the fullness of time.' He says they understand the word of truth: the gospel of their salvation, and that they're sealed with the Holy Spirit. He is speaking to all born again believers at this point.
But in verse 16 he changes. He prays for them, instead of commending their faith. He prays God may give them the spirit of wisdom and revelation in the knowledge of him -- that the eyes of their understanding might be enlightened. He wants them to know the hope of God's calling in their life -- the riches of his inheritance to them -- the greatness of his power in them -- that as the church they are raised with Christ, and have all authority in this world.
Paul doesn't see everyone who is born again as a Christian to be living in faith in Jesus. It's like he's addressing two different groups of Christians. Thus, Hebrews 6:1 talks about going on to maturity, which is more than having 'faith in God.' Our faith in God brings salvation, but Paul sees this as elementary, human faith, and not the higher level of faith he was praying for beginning in Ephesians 1:16.
WE SHOULD LIVE IN TRUTH AND FAITH
In II Timothy 3:7 Paul talks about those Christians who are 'ever learning, and never able to come to the knowledge of the truth.' They want to know more. They read and study their Bibles. But they stay in 'elementary school,' spiritually. They never graduate from 'Sunday School 101.'
Paul says God would have (1) all men to be saved, AND (2) to come into the knowledge of the truth (I Tim 2:4). It is evident that all Christians do not come into the revelation of gospel truth. "The law was given by Moses, but grace and truth came by Jesus Christ" (John 1:17). Paul says that many Christians only live in 'a form of religion, but deny the power of God.' They don't live in the gospel truth. They don't know the power of Jesus in them.
God wants us all to live in Christian beliefs, and living in truth and in faith in Jesus so that our hearts are established in grace (Heb 13:9). If established in the gospel of grace, then we are in a position to receive all that God has to give us.
If we are not so positioned in the gospel of the truth of God's grace and peace, then we are of a religious, humanistic mindset of living by laws and rules. When this is our pattern, it results in a curse (Gal 3:10). Here we are buying into some form of denomination of Christianity that is not living in truth and in faith in Jesus which produces the power of God in us (Rom 1:16).