Kevin DeYoung has a great series of four posts on Truths that Transform, Doctrines that Damn.
Here are his summary conclusions, but go read all four posts.
First off, we see that anyone who says they have a church with no doctrinal center does not have a Christian church.
Second, we see that the early church believed orthodoxy was very important, and it was more than just living the right way, it involved holding certain truths about God, Christ, and salvation.
Third, we see that orthodoxy is not a moving target. There is no indication that Paul wanted his young pastors to repaint the Christian faith for a new generation. On the contrary, there is every indication that he wanted the apostolic deposit of truth to be passed on untouched and uncorrupted.
Fourth, we see that this apostolic message was to be declared boldly and confidently, and anyone who preached a different message or led others away from this core message were to be gently opposed and strongly rebuked (somehow, I guess, we can gently oppose and strongly rebuke at the same time).
Fifth, and more to the point of this series of blog posts, we see what the essentials of the faith looked like. The gospel message that Paul preached and expected all Christian to adhere to looked something like this: God is glorious; we are sinners; and Jesus Christ is our Savior and God. Jesus Christ is the son of David and God in the flesh; he died and rose again; he ascended into heaven; he is coming again. Salvation is by sovereign grace, according to the converting power of the Holy Spirit, through faith, not according to works. Jesus Christ saves us from sin, saves us for eternal life, and saves us unto holiness.
This is the gospel of the early church. It is rooted in Scripture. It is not to be deviated from. And it must be proclaimed confidently by anyone who would lay claim to apostolic authority in his ministry.