A Prophet who is not a Messenger does not come with a new Shar^ – Law. He teaches that Law which was revealed to the Messenger before him. In other words, Allah revealed to him to follow the set of Islamic Laws of the Messenger before him. The Messenger is the one to whom a new set of Islamic Laws were revealed. Both the prophets and the prophets who are messengers (henceforth “messengers”), are ordered by Allah to convey the Revelation they receive to the people.
Allah ta^ala said in Surat al-Baqarah verse # 213:
﴿كان الناس أمةً واحدةً فبعث الله النبيين مبشرين ومنذرين﴾ سورة البقرة.
The verse means: [Mankind was of one religion; then Allah sent the prophets as bringers of good tidings and warners].