Walamma balagha ashuddahu wastawa ataynahu hukman waAAilman wakathalika najzee almuhsineen (surah Qasas: 14)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(28:14) When Moses had reached his full maturity and become full- grown, *18 We gave him judgement and knowledge; *19 thus do We reward the righteous.

Wa lammaa balagha ashuddahoo wastawaaa aatai naahu hukmanw wa `ilmaa; wa kazaalika najzil muhsineen

*18) That is, when he had attained his full mental and physical development. In this connection, different ages of the Prophet Moses have been mentioned in the Jewish traditions. Some say he was 18, others have mentioned 20 years and still others 40 years. According to the New Testament, he was 40 years old. (Acts, 7: 23). But the Qur'an does not mention any age. For the purpose of the incident being mentioned in the following verses, it is enough to know that he had attained his full maturity at that time.
*19) Hukum implies wisdom, understanding and power of judgement, and 'llm is both religious and worldly knowledge. The Prophet Moses became familiar with the teachings of his forefathers the Prophets Joseph. Jacob, Isaac and Abraham (peace be upon all of them) through his contact with his parents, and with the sciences prevalent in Egypt by virtue of his training as a prince in the king's palace. Here the gift of Hukm (wisdom) and `Ilm (knowledge) does nor refer to the gift of Prophethood, because Prophethood was bestowed on Moses several years afterwards, as is mentioned below, and has already been mentioned in Ash-Shu`araa: 21 above.
Regarding his education and training while as a prince the New Testament says: "Moses was learned in all the wisdom of the Egyptians, and was mighty in words and' in deeds." (Acts, 7: 22). The Talmud says: Moses grew up, a handsome lad, in the palace of the king: he dressed royally, was honoured by the people, and seemed in all things of royal lineage. He visited the land of Goshen daily, observing the rigour with which his brethren were treated.... Moses urged the king of Egypt to grant the men of Goshen one day of rest from the labour, in each week, and the king acceded to his request. Moses said, "If you compel them to labour steadily their strength will fail them; for your benefit and profit allow them at least one day in the week for rest and renewal of strength", And the Lord was with Moses, and his fame extended through all the land. " (H. Polano: The Talmud Selection pp. 128-29).