Are all of Paul’s teachings related to the Gospels,...

or does the Holy Spirit work through Paul and the other Apostles to add new teachings not covered in the Gospels?

This is a good question and to really give an answer, you have to know a little more about the makeup of the Bible. The first question has to be “what is the Bible in the first place?” This is a fundamental question that is critical to understand—the Bible is God’s self-disclosure (also called “revelation”) to humankind. Without this self-disclosure from God it would be impossible for humans to know enough about God to come into a relationship with Him. Through the wonder of creation, it is possible to come to a realization that there is a higher power but the book of Romans makes it clear that this knowledge is not enough to bring a human into relationship with the Creator.

The second question to answer has to do with is “what, if anything, is the central theme of the Bible?” The central thrust of the Bible is the story of God. I believe this central theme is misunderstood by many to be the salvation of humankind—while this is clearly of prime importance, it is just one facet of the story of God. The story is revealed through the different genres of the Bible such as history, narration, letters, law, wisdom, gospel, poems and hymns, and prophecy.

Gospel literally means “good news.” When people say “the gospels”, they are referring to the books of Matthew, Mark, Luke, and John. The central character in each of these gospel accounts is Jesus Christ, the Son of God. The “good news” that these books tell us of is Jesus Christ’s sacrificial death on the cross that allows us to come into a relationship with God.

Regarding your question, the account of the death of Christ for the salvation of humankind is a monumental piece of God’s story—but it is a piece of the story, not the whole story. Each book of the Bible gives us an understanding of God and his plan. This goes all the way back to creation recounted in the book of Genesis and goes to the end of God’s story, or the book of Revelation. Not trying not to oversimplify things, but you can say the other books of the New Testament teach us how we are to live in the light of the good news of Jesus and our salvation. Each book in both the Old Testament and the New Testament is a piece of this story and without them all we have is an incomplete picture of God.