A person that speaks Lashon Hara will not have his prayers answered. Imagine if a person hurts your child and then comes to you and asks for a favor. You would be disgusted to help that person after they injure your child. G-d is similar. If a person speaks Lashon Hara against one of His children, He will not want to grant your requests.
4. Be kind to yourself. Speaking badly even about yourself is unethical.
הלכות שמירת הלשון 