Why does Allah guide some disbelievers to Islam and save them from the Fire, yet not decree guidance for others, and favor some of His servants over others?

Allah knows best who deserves guidance, and He is the All-Knowing, the All-Wise, who puts everything in its proper place. Guidance and misguidance are in His hands, glory be to Him. He guides by His grace and mercy, and misguides by His justice and wisdom. He knows best where His grace and justice are to be applied, as He Almighty said: {He is most knowing of who has strayed from His way, and He is most knowing of who has been guided} [An-Najm: 30]. Reward and punishment are contingent upon adherence to the Sacred Law, both in commission and omission. One should busy themselves with seeking beneficial knowledge and refrain from delving into ambiguities.