The sufficiency of Scripture does not mean that the Scripture is all we need to live obediently. To be obedient in the sciences we need to read science and study nature. To be obedient in economics we need to read economics and observe the world of business. To be obedient in sports we need to know the rules of the game. To be obedient in marriage we need to know the personality of our spouse. To be obedient as a pilot we need to know how to fly a plane. In other words, the Bible does not tell us all we need to know in order to be obedient stewards of this world.
The sufficiency of Scripture means that we don’t need any more special revelation. We don’t need any more inspired, inerrant words. In the Bible God has given us, we have the perfect standard for judging all other knowledge. All other knowledge stands under the judgment of the Bible even when it serves the Bible. For example, the English language serves the Bible by making it accessible to readers of English. But even as English does this, it stands under the Bible and is governed by the Bible. So the English word “yes” cannot translate the Greek word for “no.” The Bible is sufficient to prevent that misuse of English.
In this way the Bible is served by our extra-biblical knowledge in many ways. For example, the word “ant” occurs twice in the Bible (Proverbs 6:6; 30:25). It is never defined. The Bible expects us to know what an ant is from our experience. But if we say that the lesson of the ant is that we should all be lazy, the Bible is sufficient to prevent that error.
So it is with language in doctrinal disputes. Non-biblical language serves the Bible by ruling out some meanings and including others. The word “trinity” and the phrase “one substance with the Father” are extra-biblical terms. But they contain essential biblical truth. To affirm with extra-biblical language that God is “one essence in three persons” (=trinity) and that the Son is “one substance with the Father” is more biblical than to use biblical language to call Christ God’s creature. The sufficiency of Scripture does not dictate the language we use to interpret the Bible; rather it governs the meaning of the language we use. For that it is wholly sufficient.
It seems that progressive fundamentalists go further than one of their heros on this issue.