So important is the tongue to teaching that James can say this in James 3:2:

We all stumble in many ways. If anyone is never at fault in what he
says, he is a perfect man, able to keep his whole body in check.

For James, proper speech indicates mastery of one’s entire self. James said something similar back in chapter one and it surprises that the suddenly brings it up. At 1:26 he said:

If anyone considers himself religious and yet does not keep a tight
rein on his tongue, he deceives himself and his religion is worthless.

A form of teaching is reduction: reducing the big idea and the big quest to the very essence. Jesus reduced the Torah to love of God and love others, and James does this as well (2:8-13), but in James 3 (and James 1:26), James reduces life to how we use the tongue.

It might be wise to ponder if the reductive principle can be reversed — does control of the tongue always indicate proper piety? And the answer would be no. But that doesn’t alter the reality that control of the tongue, in James’ context, indicates maturity or what James calls “perfection.” That is, the person who has mastered what God has called us to.

And James is interested in mastering in this context: the teacher who can control his or her tongue has the power to control the whole body, and James will now illustrate that point with an effusion of examples.