Behold also the ships - This illustration is equally striking and obvious. A ship is a large object. It seems to be unmanageable by its vastness, and it is also impelled by driving storms. Yet it is easily managed by a small rudder; and he that has control of that, has control of the ship itself. So with the tongue. It is a small member as compared with the body; in its size not unlike the rudder as compared with the ship. Yet the proper control of the tongue in respect to its influence on the whole man, is not unlike the control of the rudder in its power over the ship.
Which though they be so great - So great in themselves, and in comparison with the rudder. Even such bulky and unwieldy objects are controlled by a very small thing.
And are driven of fierce winds - By winds that would seem to leave the ship beyond control. It is probable that by the "fierce winds" here as impelling the ship, the apostle meant to illustrate the power of the passions in impelling man. Even a man under impetuous passion would be restrained, if the tongue is properly controlled, as the ship driven by the winds is by the helm.
Yet are they turned about with a very small helm - The ancient rudder or helm was made in the shape of an oar. This was very small when compared with the size of the vessel - about as small as the tongue is as compared with the body.
Whithersoever the governor listeth - As the helmsman pleases. It is entirely under his control.

Behold also the ships, which though they be so great,.... Of so large a bulk, of such a prodigious size, and are such unwieldy vessels:
and are driven of fierce winds; with great vehemence, rapidity, and swiftness:
yet are they turned about with a very small helm, whithersoever the governor listeth; the helm, or tiller of a ship, is a beam or piece of timber fastened into the rudder, and so coming forward into the steerage, where he that stands at helm steers the ship (e), who is here called the governor; or "he that directs", as the word may be rendered; that is, that steers; the word for "helm" is translated rudder in Acts 27:40, and the helm or tiller is sometimes, though improperly, called the rudder itself (f); and this is very small, in comparison of the bulk of the ship that is guided by it (g). Aristotle calls it , "a small helm", as the apostle here does, and accounts for it how large ships should be moved and steered by it. And so, though the tongue is to the rest of the body as a small helm to a large ship, yet, like that, it has great influence over the whole body, to check it when it is carrying away with the force of its appetites and passions; and so churches, societies, and bodies of Christians, which are large and numerous, and are like ships upon the ocean, tossed to and fro with tempests, driven by Satan's temptations and the world's persecution, and ready to be carried away with the wind of false doctrine, yet are influenced and directed aright by those that are at the helm, the faithful ministers of the word, who say to them, this is the way, walk in it.
(e) Chambers's Cyclopedia, in the word "Helm". (f) lb. in the word "Rudder". (g) Quaest. Mechanic. c. 5.

Not only animals, but even ships.
the governor listeth--literally, "the impulse of the steersman pleaseth." The feeling which moves the tongue corresponds with this.