16 All Scripture is inspired by God and is profitable for teaching, for rebuking, for correcting, for training in righteousness, 17 so that the man of God may be complete, equipped for every good work.Whereas this sounds good in theory, I've recently been made more and more aware that we don't do a very good job of living up to this ideal.
For example, from where do we get the idea that we're supposed to use grape juice as the drink in the Lord's Supper?
Looking throughout the Bible for hints concerning the drink used at the Passover (which is the context for the establishment of the Lord's Supper), there's no clue offered until the Gospel accounts, at which time the only clue found is that it is "the fruit of the vine".
With only this information (and that it represents the blood of Christ, given in sacrifice), doesn't it make sense that tomato juice (blood-like, from the vine) would be the best option for the drink at the Lord's Supper?
Or if you just want a fruit of the vine, and don't care about the color, we could use cantaloupe juice, or watermelon juice, or blueberry juice, or passionfruit juice, or any number of other vine fruit juices.
But we don't; we use grape juice (either fermented or not).
The point is: We use grape juice, not because it's taught in the Bible, but because it's a tradition we have inherited from some source outside of the Bible. I think extraBiblical history makes a strong case for using grape juice. But I'm just pointing out that going to extraBiblical history is not relying solely on the the Bible.
"So what," you ask?
If someone wants to use watermelon juice in the Lord's Supper, we can make no objection if we really use the Bible as our sole source of authority in such matters. To make a law that the juice must be grape juice is to teach as doctrine the commandment of men.
We do this a lot. We need to be careful.