We can actually say things that call our faith into question. We can say actually speak in ways that bring eternal punishment upon us. There is a trend among Christians to believe that we are free to think or to say whatever comes to mind since we are forgiven. But this belief is not from God. Evil thoughts and words hurt and do the devil's work.
Words can ruin reputations and careers.
They shorten and embitter life. They destroy a person's sense of self-worth, just like the angry words that led to Jesus' ultimate destruction. On the cross Jesus was suffering for every sinful thing that we, or the rest of mankind, has every thought, done, or said against God or another person. If we were to list all of the sins that caused the death of the Son of God we would have to include words that we have at one time or another carelessly or angrily spoken against God or others. Jesus didn't suffer only for sinful intentions actually acted upon, but also for sins only conceived of but never carried out, or spoken even in jest.