What is the meaning of Allah Almighty's saying: "He guides whom He wills by His mercy and He leads astray whom He wills, and you will surely be questioned about what you used to do," and does Allah lead astray or does man lead himself astray?

The Almighty's saying: (And if Allah had willed, He would have made you one nation, but He sends astray whom He wills and guides whom He wills. And you will surely be questioned about what you used to do) means that if Allah had willed, He would have made people one nation upon the true religion, but He sends astray whom He wills by His justice and guides whom He wills by His grace. And He will question them on the Day of Resurrection about their deeds. Allah has absolute will in His creation, but His will does not negate the will of those who are held accountable. Therefore, it is not permissible for a person to use Allah's will as an excuse for his misguidance, for Allah has shown him the path of good and evil and granted him the ability to choose.