John Calvin on James 3:5

And boasteth great things. The verb μεγαλαυχεῖν means to boast one’s self, or to vaunt. But James in this passage did not intend to reprove ostentation so much as to show that the tongue is the doer of great things; for in this last clause he applies the previous comparisons to his subject; and vain boasting is not suitable to the bridle and the helm. He then means that the tongue is endued with great power.

I have rendered what Erasmus has translated the impetuosity, the inclination, of the pilot or guide; for ὁρμὴ means desire. I indeed allow that among the Greeks it designates those lusts which are not subservient to reason. But here James simply speaks of the will of the pilot.

James 3:5-6

5 — Behold, how great a matter a little fire kindleth!

5 Ecce exiguus ignis quantam sylvam incendit.

6 And the tongue is a fire, a world of iniquity: so is the tongue among our members, that it defileth the whole body, and setteth on fire the course of nature; and it is set on fire of hell.

6 Et lingua ignis est, et mundus iniquitatis: sic inquam lingua constituta est in membris nostris, inquinans totum corpus, inflammans rotam nativitatis, et inflammatur a gehenna.