QUR'AN...
QUR'AN: Say: "We believe in Allah and (in) that which has been revealed to us, and (in) that which was revealed to Ibrahim. . . ": After mentioning the claim of the Jews and the Christians, Allah describes the truth - and He always tells the truth. The truth consists of the testimony of belief in One God and belief in all that was brought by the prophets - without making any distinction between them. This is what is called the Islam.
Belief in Allah was the fundamental part of that which was revealed to the prophets; yet it has been mentioned here separately. The reason is that the belief in the Creator is a natural instinct; it does not depend on prophetic proofs and arguments. After that fundamental belief, Allah mentions "that which has been revealed to us", that is, the Qur'an or the knowledge contained in it. Then He mentions "that which was revealed to Ibrahim and Isma'il and Ishaq and Ya'qub".
Thereafter is described "that which was given to Musa and 'Isa'; these two have been especially mentioned because the speech is addressed to the Jews and the Christians who call only to these two prophets, respectively. Finally the testimony includes "that which was given to the prophets". This sentence covers all the prophets and thus paves the way for the next declaration: "we do not make any distinction between any of them".
Probably the reason is this: The basic idea may be conveyed by the word, "giving", as Allah says after mentioning Ibrahim and other prophets who came before or after him: These are they to whom We gave the book and the wisdom and the prophethood (6:89). But this word does not clearly and necessarily mean "revelation"; for example, Allah says: And certainly We gave wisdom to Luqman (31:12); And certainly We gave the book and the wisdom and the prophecy to the Children of Israel... (45:16).
Now both the Jews and the Christians counted Ibrahim, Isma'il, Ishaq, Ya'qub and the tribes as following their religions respectively - the Jews claimed that those prophets were Jews; the Christians claimed that they were Christians. They believed that the true religion was the Judaism or the Christianity that was given to Musa or 'Isa respectively.