3 Behold, we put bits in the horses' mouths, that they may obey us; and we turn about their whole body.
4 Behold also the ships, which though they be so great, and are driven of fierce winds, yet are they turned about with a very small helm, whithersoever the governor listeth*.
Simply put, the tongue is compared to a mechanism that controls LARGE things in this world such as a SHIP, or a great war horse is controlled by a BIT, so the TONGUE needs to be under subjection of the person to whom it resides as it can cause many things to happen when it engages in things that it should not....
WE MUST LEARN to CONTROL OUR TONGUES and the WORDS which proceed forth. Whatever proceeds forth from the TONGUE is an indicator of what LAYS IN YOUR HEART....