Only a little more than a generation had passed since the founding of the church, yet false gospels, perversions of the truth, were making serious trouble for those early Christians. Paul was warning members of the church in Galatia not to listen to those who are trying to persuade them away from the true doctrines of God, which they had learned when the apostles had preached the true gospel to them.
After warning them in verses 8-9, Paul goes on to defend himself against the unwritten question, "How do we know that you preached us the truth?" He asks in return, "From what you've seen of me, do I try to seek the favor of men or God? Do I seem to be a men-pleaser?" Clearly, he always put the truth of God before pleasing people, and he had had to pay the price for it in persecution and peril (see II Corinthians 11:23-33). He considered these sacrifices proof that he was a true servant of God.
Then, in Galatians 1:11-12, he lets them know where the true message he had taught them came from. He was taught, he said, not by any man (verse 16), but by Jesus Christ Himself. Once God had called him on the road to Damascus, and after he was baptized, he went down to Arabia (verse 17), staying there for three years (verse 18). There, Christ taught him the truth as an apostle "born out of due time" (I Corinthians 15:8). Our Savior had a special job for Paul and wanted to give Him the same kind of instruction that He had given the Twelve.
No one knows if Christ came down and appeared to him, teaching him directly, or whether He opened Paul's mind and revealed the truth out of Scripture. However it was done, when he went up to Jerusalem three years later and talked with Peter, James, and John, he found that they agreed completely on the gospel of God (Galatians 2:9). These men understood that Paul was a fellow apostle with them and that his mission would focus primarily on the Gentiles.
By his personal history, Paul shows that he had received the same, true revelation from God that the original disciples had been given. Thus, the gospel that he taught was the same gospel that Peter, John, and the other apostles were also preaching. They all preached from the same Source: Jesus Christ. Our beliefs should rest on that same foundation, which is now printed in our Bibles. Notice Ephesians 2:19-22:
Now, therefore, you are no longer strangers and foreigners, but fellow citizens with the saints and members of the household of God, having been built on the foundation of the apostles and prophets, Jesus Christ Himself being the chief cornerstone, in whom the whole building, being joined together, grows into a holy temple in the Lord, in whom you also are being built together for a dwelling place of God in the Spirit.
In terms of revelation from God, this passage informs us that a true understanding is built on the foundation of the apostles and prophets. In the past, God revealed certain things to the prophets in Old Testament times and to the apostles in New Testament times, and they wrote those things down for our learning (see Hebrews 1:1; Romans 15:4; I Corinthians 10:11). Jesus Christ is called "the chief cornerstone" because He is the true Foundation and Source of all revelation. He is the One who joins all the revelation together and makes it work. We, then, having this sure foundation, not only learn the truth, but also grow by it into the image of Christ.
The apostle continues in Ephesians 3:
For this reason I, Paul, the prisoner of Christ Jesus for you Gentiles—if indeed you have heard of the dispensation of the grace of God which was given to me for you, how that by revelation He made known to me the mystery (as I have briefly written already, by which, when you read, you may understand my knowledge in the mystery of Christ), which in other ages was not made known to the sons of men, as it has now been revealed by the Spirit to His holy apostles and prophets. (Ephesians 3:1-5)
Paul uses the subject of God's grace toward the Gentiles as a way to get across, not only that he preached the true gospel, but also how truth comes into the church of God. It is very simple: God revealed something to him, and he, then, wrote it down in a few words, so that we could read and comprehend his understanding of the mystery of God's way. That is how it works: God inspired a prophet or an apostle, and he wrote it down. Over time, it became Scripture, and now we read it, using the Holy Spirit that God has given us, to understand the truth.
At the end of the Bible, in Revelation 22:18-19, John warns the reader not to add to or take away from the words written in the Book, something the false teachers in Galatia were obviously doing. Essentially, he is telling us that revelation from God to man is closed; the canon of Scripture is complete. What we need to know for salvation is in the finished work of the Bible. Anyone who claims to have a new revelation, that he has some "new truth" beyond Scripture, is a false teacher, one of those who "pervert the gospel of Christ" (Galatians 1:7).
So the Bible is the collected writings of the apostles and prophets to whom God gave His precious revelation for all of us to learn and use. God's converted children do not need any advanced degrees, courses in higher thinking and logic, or any kind of worldly help to understand God's truth. All they need is the Word of God and a humble mind that can reason normally, and God, by the gifts of His Spirit (which includes a faithful ministry; Ephesians 4:11), provides the understanding.