What is the wisdom behind the difference in the reading of Hafs and Warsh regarding the words (عليهُ/عليهِ), (وَمَنْ/وَمَنَ), and (فَسَيُؤْتِيهِ/فَسَنُوتِيهِ) in verse 10 of Surat Al-Fath?

The variations in Quranic readings (qira'at) are differences of diversity and variation, not contradiction. This means that each reading adds a new meaning and expands upon existing meanings, much like the multiplicity of verses.

Regarding the verse ﴿وَمَنْ أَوْفَى بِمَا عَاهَدَ عَلَيْهُ اللَّهَ فَسَيُؤْتِيهِ أَجْرًا عَظِيمًا﴾ [And whoever fulfills what he has covenanted with Allah – He will surely give him a great reward], Hafs alone recited with a ḍamma on the hā (عَلَيْهُ), his argument being to preserve the original form of the hāʾ. Meanwhile, the majority recited with a kasra on the hā (عَلَيْهِ) due to its proximity to the yāʾ. Among the merits of the ḍamma in this verse is the glorification of the majestic name of Allah and its consistency with the glorification of the covenant.

As for the reading of (فَسَيُؤْتِيهِ), Abu Amr, the Kufans, and Ruwais recited with the yāʾ (فَسَيُؤْتِيهِ), which refers back to the majestic name of Allah. The rest recited with the nūn (فَسَنُؤْتِيهِ), which is a shift from the third-person style to the first-person.