To keep a cannon from becoming a liability to your own forces, however, you have to ensure that it keeps pointing in the right direction. The recoil from propelling heavy projectiles forward at a high rate of speed causes the cannon to lurch backward, and often slightly to one side or the other. If not corrected, this would obviously result in disastrous friendly-fire casualties. To minimize this risk, soldiers would sometimes stake down their cannons to keep them from getting too far off target.
Okay, so what does this have to do with Ephesians 4:15?
I think our mouths can be analogized to cannons. Properly aimed, my mouth can do a great deal of damage to the enemy. I can speak words of truth that demolish Satan's strongholds and reduce falsehood to rubble. I can also launch projectiles of love that batter down stoney defenses and open the way for the healing invasion of grace. But our mouths also have the potential to cause tremendous harm to our own side. To prevent friendly fire, they must be chained down with the twin restrains of a loving manner and adherence to biblical truth.
If I launch into battle with a fierce commitment to biblical accuracy, but without the restraint of a loving manner, not only am I not going to be very effective against the enemy, but just like a cannon that is carelessly tied down on only one side, and eventually works its way around until it is launching cannonballs at its own side, sooner or later I am going to start firing broadsides into the ranks of my fellow soldiers. Likewise, if my speech is carefully calculated to avoid offending anyone, but I cast off the restraint of biblical accuracy, I will also inevitably end up hurting my own side.
Friends, we're in a real battle; a life and death struggle over who God is, and what He's like. It's a battle for the hearts and minds of men, a battle of ideas and belief - and words are the ammunition. The words we speak will make an impact - on one side or the other! Let's make sure the words that come out of our mouths are both truthful, and loving.