18. This sentence can have several meanings:
(1) That the Messengers continued to come to them one after the other.
(2) That the Messengers tried in every way to make them understand the truth and did not leave any stone unturned to bring them to the right path.
(3) That the Messengers came to them in their own country as well as in the adjoining countries.
19. That is, if Allah had disapproved of our religion, and had willed to send a messenger to us to keep us away from it, He would have sent the angels. As you are not an angel but a man like us, we do not believe that you have been sent by God, and sent for the purpose that we give up our religion and adopt the way of life that you are presenting. The disbelievers’ saying that they deny, what you have been sent with, was only sarcastic. It does not mean that they believed him to have been sent by God and then denied what he said. But this is a sarcastic expression of the type that Pharaoh had uttered before his courtiers about the Prophet Moses (peace be upon him): This messenger of yours, who has been sent to you, seems to be utterly mad. (Surah Ash-Shuara, Ayat 27). For further explanation, see (E.N. 11 of Surah YaSeen).