Imagine if a person has a barrel of very expensive wine, but he puts a dirty spigot on the barrel. The wine will taste disgusting when it comes out because of the dirt on the spigot. A person’s mouth is like a spigot. If a person davens from the heart with beautiful concentration, but his mouth speaks filthy things, his prayers become dirty. A person should always be careful of what comes out of his mouth, so he does not “dirty” his prayers.
4. Be kind to yourself. Speaking badly even about yourself is unethical.
הלכות שמירת הלשון 