There is a difference between apostolic doctrine and true doctrine. This is because the apostles upon occasion taught error.
Our authority for knowing truth depends on apostolic teaching. We have no other choice than to accept their teaching; after all, they learned it from Jesus himself. But we need to discover the things they added or changed, and reject these.
We should wonder how to obtain true doctrine if the apostles can't completely be trusted? The answer is to see how the flow of time answers things, the test of time. For example, the idea that the body is bad has had horrible results, and the idea that Christians should have everything in common was such a bad idea even the apostles soon abandoned it.
Here are the true doctrines...
- God as Trinity, creator of physical realm and spiritual realm.
- Jesus is deity, Son of God, second person of the Trinity, who took on human nature and redeemed it.
- Original sin infected the human race requiring redemption by God's grace.
- Jesus died by crucifixion to redeem humanity; he rose from the dead conquering death.
- Salvation requires repentance of sin, turning away from it, and calling out to God in faith, begging for forgiveness.
- Christian leaders are to teach truth, defend the faith, and shepherd the flock of Christians.
- Christians are to form communities of fellowship, prayer, and worship. This requires leadership.
- There is such a thing as the "Church" consisting of leadership, true teaching, evangelism, fellowship, etc. Over-emphasizing the institutional church has had bad effects and was never intended by Jesus.
- Jesus established the Eucharist as a form of corporate worship; it is not merely symbolic (unless that's all you believe it to be).
- Jesus will come again at his second and final coming. After this, the universe as we know it will change significantly as sin and death will be defeated and the redeemed will inhabit the new heavens and new earth for all eternity in resurrected bodies.
- Those who reject God's love will spend eternity in the lake of fire. We should pray there are none in this category.
- We are to fix our eyes upon Jesus.