Allah said,

(And when it is said to them), meaning, the Jews and the People of the Book,

(Believe in what Allah has sent down) to Muhammad, believe in and follow him,

(They say, "We believe in what was sent down to us.'') meaning, it is enough for us to believe in what was revealed to us in the Tawrah and the Injil, and this is the path that we choose,

(And they disbelieve in that which came after it).

(while it is the truth confirming what is with them) meaning, while knowing that what was revealed to Muhammad ,

(it is the truth confirming what is with them). This means that since what was sent to Muhammad conforms to what was revealed to the People of the Book, then this fact constitutes a proof against them. Similarly, Allah said,

(Those to whom We gave the Scripture (Jews and Christians) recognize him (Muhammad) as they recognize their sons) (2:146). Allah said next,

("Why then have you killed the Prophets of Allah aforetime, if you indeed have been believers'').

This means, "If your claim that you believe in what was revealed to you is true, then why did you kill the Prophets who came to you affirming the Tawrah's Law, although you knew they were true Prophets You killed them simply out of transgression, stubbornness and injustice with Allah's Messengers. Therefore, you only follow your lusts, opinions and desires.'' Similarly, Allah said,

(Is it that whenever there came to you a Messenger with what you yourselves desired not, you grew arrogant Some you disbelieved and some you killed.)

Also, As-Suddi said, "In this Ayah, Allah chastised the People of the Book,

(Say (O Muhammad to them): "Why then have you killed the Prophets of Allah aforetime, if you indeed have been believers'').''

(And indeed Musa came to you with clear proofs) meaning, with clear signs and clear proofs that he was the Messenger of Allah and that there is no deity worthy of worship except Allah. The clear signs -or miracles- mentioned here are the flood, the locusts, the lice, the frogs, the blood, the staff and the hand. Musa's miracles also include parting the sea, shading the Jews with clouds, the manna and quails, the gushing stone, etc.

(yet you worshipped the calf) meaning, as a deity instead of Allah, during the time of Musa. Allah's statement,

(after he left) after Musa went to Mount Tur to speak to Allah. Similarly, Allah said,

(And the people of Musa made in his absence, out of their ornaments, the image of a calf (for worship). It had a sound (as if it was mooing)) (7:148).

(and you were Zalimun) meaning, you were unjust in this behavior of worshipping the calf, although you knew that there is no deity worthy of worship except Allah. Similarly, Allah said,

(And when they regretted and saw that they had gone astray, they (repented and) said: "If our Lord have not mercy upon us and forgive us, we shall certainly be of the losers'') (7:149).

(93. And (remember) when We took your covenant and We raised above you the Mount (saying), "Hold firmly to what We have given you and hear (Our Word).'' They said, "We have heard and disobeyed.'' And their hearts absorbed (the worship of) the calf because of their disbelief. Say: "Worst indeed is that which your faith enjoins on you if you are believers.'')