What is the meaning of "What Allah wills, comes to be; and what He does not will, does not come to be"?

The meaning of "What Allah wills, comes to pass; and what He does not will, does not come to pass" is that everything Allah has decreed and willed must inevitably occur, and whatever He has not decreed will not come to pass. This aligns with the belief in divine decree (Qadar), for "what has befallen you was not to miss you, and what has missed you was not to befall you." That is, what Allah has decreed to happen will certainly happen, and what He has decreed not to happen will not happen. It is mentioned in the Prophet's (peace and blessings be upon him) advice to Ibn Abbas: "And know that if the whole nation were to gather to benefit you with something, they would not benefit you except with that which Allah has already written for you. And if they were to gather to harm you with something, they would not harm you except with that which Allah has already written upon you. The pens have been lifted, and the scrolls have dried."