He now explains the evils which proceed from the neglect of restraining the tongue, in order that we may know that the tongue may do much good or much evil, -- that if it be modest and well regulated, it becomes a bridle to the whole life, but that if it be petulant and violent, like a fire it destroys all things. He represents it as a small or little fire, to intimate that this smallness of the tongue will not be a hindrance that its power should not extend far and wide to do harm.

Even so the tongue is a little member - Little compared with the body, as the bit or the rudder is, compared with the horse or the ship.
And boasteth great things - The design of the apostle is to illustrate the power and influence of the tongue. This may be done in a great many respects: and the apostle does it by referring to its boasting; to the effects which it produces, resembling that of fire, James 3:6; to its untameableness, James 3:8-9; and to its giving utterance to the most inconsistent and incongruous thoughts, James 3:9-10. The particular idea here is, that the tongue seems to be conscious of its influence and power, and boasts largely of what it can do. The apostle means doubtless to convey the idea that it boasts not unjustly of its importance. It has all the influence in the world, for good or for evil, which it claims.
Behold, how great a matter a little fire kindleth! - Margin, "wood." The Greek word ὕλην hulēn, means a wood, forest, grove; and then fire-wood, fuel. This is the meaning here. The sense is, that a very little fire is sufficient to ignite a large quantity of combustible materials, and that the tongue produces effects similar to that. A spark will kindle a lofty pile; and a word spoken by the tongue may set a neighborhood or a village "in a flame."

Boasteth great things - That is, can do great things, whether of a good or evil kind. He seems to refer here to the powerful and all commanding eloquence of the Greek orators: they could carry the great mob whithersoever they wished; calm them to peaceableness and submission, or excite them to furious sedition.
Behold, how great a matter - See what a flame of discord and insubordination one man, merely by his persuasive tongue, may kindle among the common people.

Even so the tongue is a little member, and boasteth great things. (5) Behold, how great a matter a little fire kindleth!
(5) On the contrary part he shows how great inconveniences arise by the excesses of the tongue, throughout the whole world, to the end that men may so much the more diligently give themselves to control it.

Even so the tongue is a little member,.... Like the bit in the horse's mouth, or like the helm of a ship.
And boasteth great things: and does them; for this word may be taken in a good sense: a bridled and sanctified tongue, that is influenced by the grace of God, and directed by the Spirit of God, as it speaks great and good things, it has great power, weight, and influence: the tongue of the just is as choice silver, and the lips of the righteous feed many, Proverbs 10:20, the Gospel, as preached by Christ's faithful ministers, who are the church's tongue, when it comes not in word only, but in power, is the power of God unto salvation: faith comes by hearing it, and hearing by this word; by it souls are convinced, converted, and comforted, enlightened, quickened, and sanctified.
Behold, how great a matter a little fire kindleth; what vast quantities of wood, large forests, stately buildings, and populous towns and cities, are at once seized on by a little fire, a few sparks, and in a short time burnt down, and utterly destroyed. One of the proverbs of Ben Syra is,
"burning fire kindles great heaps;''
suggesting, that an evil tongue does great mischief, as did the tongue of Doeg the Edomite, as the gloss upon it observes: from hence the apostle passes to consider the abuse or vices of the tongue.

boasteth great things--There is great moment in what the careless think "little" things [BENGEL]. Compare "a world," "the course of nature," "hell," James 3:6, which illustrate how the little tongue's great words produce great mischief.
how great a matter a little fire kindleth--The best manuscripts read, "how little a fire kindleth how great a," &c. ALFORD, for "matter," translates, "forest." But GROTIUS translates as English Version, "material for burning": a pile of fuel.

Boasteth great things - Hath great influence.