I was reading Psalm 52 this morning, which says "Your tongue devises destruction, like a sharp razor, working deceitfully." I had to ask myself, how is the tongue like a razor? A razor can do a lot of damage to the body, but the tongue hardly compares.
Normally I think of this in terms of hurting someone's reputation or feelings. But deceit, slander, and malice can do damage even if you're tough enough to not get your feelings hurt, because the body this razor attacks is not that of the individual, but that of the community.
A physical razor can amputate body parts, but a razor made of words can amputate people from one another. Deceit and slander turn people who should be unified against each other. The love and affection forged by years of fellowship can quickly be disrupted by malicious words, even those of a third party.
Beware of those who wield words like weapons, rather than "speaking the truth in love", encouraging others, and building others up. Community is fragile, and needs to be nurtured and protected.