If we put bits into the mouths of horses so that they obey us, we guide their whole bodies as well.
3 We put bits in the horses’ mouths. By these two comparisons he proves that a great part of true perfection is in the tongue, and that it exercises dominion, as he has just said, over the whole life. He compares the tongue, first, to a bridle, and then to a helm of a ship.
The foregoing chapter shows how unprofitable and dead faith is without works. It is plainly intimated by what this chapter first goes upon that such a faith is, however, apt to make men conceited and magisterial in their tempers and their talk. Those who set up faith in the manner the former chapter condemns are most apt to run into those sins of the tongue which this chapter condemns.
Commenting on James 3:1-12
Behold, we put bits in the horses' mouths,.... By this, and the following simile, the apostle not only expresses the smallness of that member of the body, which is like the bit in the horse's mouth, and the helm of a ship, but the good use of it, and the great influence it has over the whole body.