The tongue is a fire
The Book of James says: "Look at the ships also, though they are so great and are driven by strong winds, are still directed by a very small rudder wherever the inclination of the pilot desires. So also the tongue is a small part of the body, and yet it boasts of great things. See how great a forest is set aflame by such a small fire!" and "For judgment will be merciless to one who has shown no mercy; mercy triumphs over judgment."
What does this mean? Our words can get us in trouble very easily, and if I lash out against someone else, I can expect to get the same in return. If I do it regulary, I should expect it to fly back in my face regularly.
Even if what we want to slam someone with is true, it doesn't give us the right to use that truth to crush them. Unless we want others to treat us with the same severity. I know I don't want to be called out for my many faults. That means I need to show mercy when I see the faults (whether genuine or perceived) of others. If I feel I need to confront someone with something, there is a way to do it without humiliating them in front of others.
Jesus forgave sinners of every variety and told them to stop what they were doing, but the only people he ever jumped on were those who were extremely religious and held themselves up as being better than anyone else.
Go in peace, and pray for me, a sinner.