(And Musa said: “O Fir`awn! Verily, I am a Messenger from the Lord of all that exists”.) meaning Musa said, `the one Who sent me is the Creator, Lord and King of all things,’
(“Proper it is for me that I say nothing concerning Allah but the truth. “) `It is incumbent and a duty for me to convey only the Truth from Him, because of what I know of His might and power.’
(“Indeed I have come unto you from your Lord with a clear proof.”) `I brought unequivocal evidence that Allah gave me to prove that I am conveying the truth to you,’
(“So let the Children of Israel depart along with me.”) means, release them from your slavery and subjugation. Let them worship your Lord and their Lord. They are from the offspring of an honorable Prophet, Isra’il, who is Ya`qub son of Ishaq son of Ibrahim, the Khalil (intimate friend) of Allah.
(Fir`awn said: “If you have come with a sign, show it forth, if you are one of those who tell the truth.”) Fir`awn said, `I will not believe in what you have said nor entertain your request’. Therefore, he said, `if you have proof, then produce it for us to see, so that we know if your claim is true.’