Be not many teachers (μη πολλο διδασκαλο γινεσθε). Prohibition with μη and present middle imperative of γινομα. "Stop becoming many teachers" (so many of you). There is thus a clear complaint that too many of the Jewish Christians were attempting to teach what they did not clearly comprehend. There was a call for wise teachers (verses James 3:13), not for foolish ones. This soon became an acute question, as one can see in 1Cor 12-14. They were not all teachers (1. Corinthians 12:28; 1. Corinthians 14:26). The teacher is here treated as the wise man (James 3:13-18) as he ought to be. The rabbi was the teacher (Matthew 23:7; John 1:38; John 3:10; John 20:16). Teachers occupied an honourable position among the Christians (Ephesians 4:11; Acts 13:1). James counts himself a teacher (we shall receive, James 3:1) and this discussion is linked on with James 1:19-27. Teachers are necessary, but incompetent and unworthy ones do much harm.
Heavier judgment (μειζον κριμα). "Greater sentence." See Mark 12:40; Luke 20:47 for περρισοτερον κριμα (the sentence from the judge, Romans 13:2). The reason is obvious. The pretence of knowledge adds to the teacher's responsibility and condemnation.