قَالَ يقَوْمِ اتَّبِعُواْ الْمُرْسَلِينَ

(He said: "O my people! Obey the Messengers.") -- he urged his people to follow the Messengers who had come to them.

اتَّبِعُواْ مَن لاَّ يَسْـَلُكُمْ أَجْراً

The addressee here could be his own people where calling Allah Ta’ ala their Lord was to express a reality - though, they did not accept it. Then, it could also be that this address is to the messengers and the purpose of saying: إِنِّي آمَنتُ بِرَ‌بِّكُمْ فَاسْمَعُونِ (listen to me) may be that they should hear what he was saying and bear witness before Allah that he was a believer.