Allah tells us what He commanded His servant, son of `Imran and Messenger Musa, peace be upon him, who spoke with Him, to do, when He called him from the right side of the mountain, and conversed with him, and chose him, sent him, and commanded him to go to Fir`awn and his people. Allah says:
(And when your Lord called Musa: "Go to the people who are wrongdoers. The people of Fir`awn. Will they not have Taqwa" He said: "My Lord! Verily, I fear that they will deny me, And my breast straitens, and my tongue expresses not well. So send for Harun. And they have a charge of crime against me, and I fear they will kill me.") So, Musa asked Allah to remove these difficulties for him, as he said in Surah Ta Ha:
That you must send the children of Isra'i1 with us". (26:17)
Bani Isra'il were the residents of Syria. They wanted to go back to their land but the Pharaoh would not let them. This way four hundred years had passed and they were living in his bondage like slaves. At that time they were six hundred and thirty thousand in number. Sayyidna Musa (علیہ السلام) when presented the message of Truth to the Pharaoh, he also asked him to stop all the cruelties he had perpetrated over Bani Isra'il and to let them go to their homeland. (Qurtubi)
One chosen by God to represent Him is in every way under His protection. Moreover, he is given some special signs which indicate clearly that his mission is an affair of God. But, in spite of that, man has gone so far in transgression as not to admit this. The Quran does not specify the details of the demand made by Moses on Pharaoh with regard to the Children of Israel. But the Torah elaborates upon the subject in the following sections: Exodus 4/18, 5/1 , 8/25-27 . According to the description in the Bible, it appears that this journey of Moses was not for the purpose of migration but for instruction. In Egypt, the cow was considered holy. Due to this centuries-old tradition, even the the Children of Israel had been influenced by this belief. Now, Moses wanted to take the Children of Israel out of the polytheistic atmosphere of Egypt for a few days, keep them in a pure atmosphere and re-educate them.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.