” People sometimes say that Scripture is sufficient for theology, but not for other areas of life, like science, history, plumbing, politics, car repairs. But that idea misunderstands the sufficiency of Scripture. Remember always:
Scripture is sufficient as the word of God. It gives us all the words of God we will ever need. So Scripture contains all the word of God we need for theology—but also for ethics, politics, the arts, plumbing and car repair.
Certainly for all these disciplines we need knowledge from outside Scripture too. That’s even true of theology. Theologians need, for example, to know the rules of Hebrew Grammar; but Scripture doesn’t give these to us. They need to know the history of the ancient world; but Scripture only gives us part of that history. So in order to use the Bible, we need to know things outside the Bible.
That’s also true in ethics. For example, the Bible doesn’t mention abortion. We have to learn what abortion is from extra-biblical sources. But Scripture does say some things about murder, and about unborn human life. When we bring the biblical principles together with our extra-biblical knowledge of what abortion is, it becomes pretty obvious that “thou shalt not murder” implies “thou shalt not abort.”
The basic point to be remembered here is that no kind of knowledge from outside the Bible is worthy to be added to Scripture. That includes the traditions of the Roman church, claims of contemporary prophets, and even the confessions & traditions of the Protestant denominations. ”
John Frame
Gralefrit Theology 