First off, let's present the verse in question:
Let not many of you become teachers, my brethren, knowing that as such we will incur a stricter judgment. (NASU)
Second, I know of no one, not even the most highly educated man, who has a complete grasp of the bible. Yet every time I hear this verse (brought up by a preacher or teacher) they always interpret it to mean God will hold them accountable based on how accurately (or inaccurately) they deduced the meaning of whatever scripture they were teaching on a given day. That's true. A lot of false teachers will be sweating at the Judgment Seat of Christ. That said, if God were to judge us on how well we knew the Bible, we'd all be in serious trouble. This is what these guys mean when they stand up there and say things like, “I'm taking on an awful responsibility just by being up here teaching you these things.” Pious and totally inaccurate.
The apostle Peter qualifies what James wrote:
Paul...wrote to you...in which are some things hard to understand, which the untaught and unstable distort, as they do also the rest of the Scriptures, to their own destruction. (2 Peter 3:15-16)
The context seems to suggest a deeper motive: the error of unprincipled men. (vs. 17) These are folks who are mishandling God's word out of some dark motive. (See 1 Pet. 2:10ff)
The first rule of exegesis is context. Always look at a verse's context when determining the meaning. What is James speaking of immediately following verse 1? The tongue and how much trouble it causes when not controlled. When you get all the way down to chapter 4, he says, “What is the source of quarrels and conflicts among you?”
Quarreling involves the tongue, not bad teaching. Is accurately understanding scripture the reason for limiting the number of teachers? I think the better answer involves hypocrisy, not how intelligent someone is. Note Jesus' words:
The teachers of the law and the Pharisees sit in Moses' seat. So you must obey them and do everything they tell you. But do not do what they do, for they do not practice what they preach. (Matt 23:2-3) NIV
That's why the James writes about the tongue. Many bible academicians claim that the only way to not suffer the stricter judgment is to get a bible college degree so you won't mishandle the word of truth. Yet a college degree is no guarantee against error. Moreover, it falsely assumes that teaching only takes place in a formal bible study or “worship” hour. In reality, most practical and important bible discussions, if you will, take place in the home, around campfires, in bed late at night. It's not always about you, preacher!
This brings up one of the unfortunate side effects that “only the preacher” (or designated teacher) should be leading the lesson. The majority of folks would rather invite someone to church to get their questions answered because they themselves are woefully ignorant of what the bible says.
Though by this time you ought to be teachers, you need someone to teach you the elementary truths of God's word all over again. (Heb 5:12)
The Hebrew writer was telling his audience, “You guys need to learn the truths of God's word and quit mucking around with basic principles!” In an ideal setting the folks sitting in the pews should gradually reach an understanding of the bible that equals or comes close to that of their teacher's. This is not the case, however. I've sat in churches all my life and seen gray heads who had spent years in church and still failed to grasp much of the Bible. Their attitude is: “I know enough to be saved and that's good enough.” On the other hand, the teacher never expects the students to reach his level, and the students forever remain students.
The arrangement of one person forever being the teacher or preacher, and the clergy forever being the learners seems to be the paradigm in today's Christian churches. It's a good device for keeping out the false teachers, but it has the unfortunate side effect of limiting truth to only what the leader says. What the class contributes is irrelevant, unless you've got a college degree. What the preacher says is all important and thus under tighter scrutiny by the Almighty. We've got enough problems with the teacher risking his very soul, much less everyone else's.