Tafsir of Al-Fath 48:28

هو الذي أرسل رسوله بالهدى ودين الحق

He it is Who has sent His Messenger with guidance and the religion of truth, with beneficial knowledge and righteous good deeds. Indeed, the Islamic Shari`ah has two factors, knowledge and deeds. The true religious knowledge is by definition true, and the accepted Islamic acts are by definition accepted. Therefore, the news and creed that this religion conveys are true and its commandments are just,

ليظهره على الدين كله

that He may make it superior to all religions. i.e. all the religions of the people of the earth, Arabs and non-Arabs alike, whether having certain ideologies or being atheists or idolators.

وكفى بالله شهيدا

And All-Sufficient is Allah as a Witness. that Muhammad is His Messenger and that He will grant him victory. Allah the Exalted and Most Honored has the best knowledge