(أَفَغَيْرَ اللَّهِ أَبْتَغِي حَكَمًا ) ) Then is it other than Allah I should seek as judge): Allah (swt) is the One Who legislates and judges between people in their cases. As He is their Creator, He (swt) knows what is good for His (swt) creations and what is not. So, this question: (Then is it other than Allah I should seek as judge) means that we shall not seek a judge other than Allah (swt).

( وَهُوَ الَّذِي أَنزَلَ إِلَيْكُمُ الْكِتَابَ ) (while it is He who has revealed to you the Book): Meaning, Allah (swt) has revealed the book to you, O Mohammad (saws), so that you will be a judge amongst them, and this book will be guidance for them.

(مُفَصَّلًا) (explained in detail): This book explains every ruling and every judgement in this life.

( وَالَّذِينَ آتَيْنَاهُمُ الْكِتَابَ يَعْلَمُونَ أَنَّهُ مُنَزَّلٌ مِّن رَّبِّكَ بِالْحَقِّ ) (And those to whom We [previously] gave the Scripture know that it is sent down from your Lord in truth): The Jews who lived in Al-Madinah Al-Munawwarah knew that the truthfulness of the Holy, because all descriptions of the prophet – peace be upon him – were mentioned in their Torah, along with everything related to his (saws) message.

( فَلَا تَكُونَنَّ مِنَ الْمُمْتَرِينَ ) (so never be among the doubters): Although He is speaking to the prophet, peace be upon him, this speech is addressed to the nation of the Prophet, peace be upon him. Therefore, the meaning is, do not be among the doubters and think positively of Allah (swt).