Chapter 6 is a chapter of digression, which picks up an exhortation from chapter 5 about professing believers who are as babes with the word, and have not advanced beyond the first steps of salvation. Among God’s people there are those who are not advancing, or who did advance but they do not advance anymore.
There is a foundation to the Christian faith. What is the foundation? It is Christ, and that means that the foundation is the word, because Christ is the word, the eternal Son everlastingly with the Father, appointed within the triune Godhead to reveal truth to mankind. His word of revelation is also the foundation; both are. We are talking about the foundation of Christian truth, the foundation of repentance. As Christians we believe that knowledge has a foundation, and that foundation must be revealed by God. There is a science of knowledge, epistemology, in the world: the philosophy of knowledge. Does knowledge have a structure? Can it be plotted and charted? Can it be framed in propositions? Does it have a shape and a certainty? This is the great debate of epistemology and the philosophies that flow out of that. But all is pointless and hopeless unless there is a given foundation. God must speak into the world, and he must provide the foundation for all knowledge. We can investigate all kinds of phenomena and try to discover how they work to the best of our ability, but to fit them into a total picture requires revelation from God.
Sadly, some people tend to rejoice in knowledge only. But maturity includes conduct and behaviour, and there should be discernment among believers. Remember the last verse of the previous chapter: ‘Strong meat belongeth to them that are of full age, even those who by reason of use have their senses exercised to discern both good and evil’. You cannot really advance with deep appreciation of the knowledge and deep understanding, unless there is development in character and behaviour, so that you know how to choose between good and evil, and some people advance in doctrine, but there is no accompanying development of life and godliness, and so they do not really understand deeply the things they theoretically learn.
Tyndale and the old translators used to translate this a little differently and would say something like ‘leaving the first words pertaining to the doctrine Christ’ and that would be a more literal translation. Principles is perfectly good in our version because we understand by it, first principles. Modern versions tend to go for ‘elementary teachings’ about Christ, words to that effect, and that's a fair way of translating it except that, for most people, ‘elementary’ tends to mean simple, rather than first or basic steps of understanding, and so the old-fashioned term ‘principles’ may be better, because the Greek is speaking about the first words we learn about Christ. They are first, but they are not elementary. We leave them in the sense that we don't remain only with them, but the very fundamental truths of the gospel that save the soul, we enjoy and we investigate and examine all our Christian lives. They are deep things and wonderful things. As we go on, we learn more about even the basic truths of salvation.
The question arises, ‘How can we be so certain that the Bible is revelation from heaven?’ We are certain in two ways. There is one very sure way; It’s a divine way, and then there is another way. It’s less important, but it's quite precious to us, and helpful to us. Because God has made a rational world well then the distinctiveness and the uniqueness and the divine nature of Scripture can be established by observation, and by rational examination. But the most important thing is the God given means by which we know that this is his truth, and that is by spiritual illumination. There is a spiritual illumination takes place in the life of every person whom God brings to himself. Because of this, the person becomes certain and convinced that this is God's revelation of truth, and it makes perfect sense to him. He doesn't understand all of it. There's a lot to study, but overall it comes with a powerful moral demand upon him. Suddenly your mind was changed, not so much changed by anybody presenting you with arguments or evidence. It was just changed, and you looked at it differently, and you understood things in it you had not understood before. It comes across with the force of truth and reality. That is the most important thing. It will not greatly impress an unbeliever, but it does to you, because you've experienced it. But there are rational evidences, and many of them, and we often rehearse them in different ways, even teaching them to the children – the Bible’s unity of purpose, consistency, the character of its writers, the detailed prophecy, its power in individual lives.