This means, if they were to believe in what you all believe in, they will be guided to the Truth. However, if they reject and turn away, then they are in great disagreement with you and in great opposition. So, do not be concerned, Oh Muhammad, over what comes to you from them. For surely, they will conspire against you, try to poison you, rally the disbelievers against you, break their covenants with you and eventually they will try to kill you. However, Allah will protect you from them, and Allah is enough for you.
﴾أَلَيسَ اللَّهُ بِكافٍ عَبدَهُ﴿
“Isn’t Allah enough for His servant?” [Surah Az-Zumar: 36]
and He is all Hearing of whatever they say, all Knowing of whatever they do.