It's helpful advice to know that we can't unsay a cruel word. While what we say can always be forgiven, it can never be forgotten. That's why Paul reminds us in Colossians 4:5-6:
"Be wise in the way you act toward outsiders; make the most of every opportunity. Let your conversation be always full of grace, seasoned with salt, so that you may know how to answer everyone." - Colossians 4:5-6
Back in those days, salt was valuable enough to be used as money, and was treasured for its ability to preserve and flavor foods. In the same way, a Christian's speech should be helpful and valuable, ''flavored'' differently from the speech of non-believers, and preserving the message of Christ.
You never know what people are going through and somebody you encounter today may need those graceful words. With God’s grace flowing through us, our words can be tools of grace God uses to build up, encourage, and edify.