Demons KNOW that God is real and that He is alive. They deal with Him on a daily basis. Satan himself must go to God to accuse the brethren which the word says he does. They believe, but they do not accept Him as Lord of Lords and King of Kings. The practicing christian believes in God, in His word, in His Son, and in His Power. He is Lord the their lives and He is the King in their hearts. They are dedicated to Him and want to do all they can to spread the gospel and to do His will. The non practicing christian? I don't know that they have ever made Him Lord of their lives. He is apparantly not the number one priority in their lives. They may have been introduced, but are lacking a real relationship with HIM.