Tafsir of An-Nahl 16:93

{And if Allah had willed, He could have made you one nation} Following a single, Muslim path, by way of compulsion and necessity—and He is capable of that.

{But He lets astray whom He wills} Meaning: He abandons the one whom He knows will choose disbelief and persist in it.

{And He guides whom He wills} Meaning: He grants grace (luṭf) to the one whom He knows will choose faith.

This means that He has based the matter upon choice, and upon that which makes one deserving of grace, abandonment, reward, and punishment. He did not base it upon compulsion, for which one would deserve none of those things. He confirmed this with His saying:

{And you will surely be questioned about what you used to do} For if He were the one compelling them toward misguidance or guidance, He would not have established for them deeds for which they would be questioned.

{And do not take your oaths as a deception between you, lest a foot slip after it was firmly planted, and you taste evil because you hindered [people] from the way of Allah, and you will have a great punishment.}