Gabriel is an angel. In the following verse, he is mentioned separately from the Angels. What is the reason for this?

Whoever becomes an enemy of Allah, and for His angels, and His Messengers, and Gabriel, and Mikail, thus truly Allah is enemy for disbelievers.  (2:98)

The word Gabriel is mentioned separately because the Jews showed great disregard to him and respected Michael. They are told that both are Allah’s angels and showing disrespect to one is like showing disrespect to all.

In the words of Abdu’l-Mājid Daryābādī:

The Jewish conception is that Gabriel stands nearest to Michael but does not equal him in rank. (JE. V. p. 541)1 , and is the ‘angel of heavenly vengeance and of fire’. (JE. I. p. 593)2. The Jews considered Michael to be their national guardian, and made a grievance of the agency of Gabriel who according to them was the messenger of wrath and punishment. It was Michael, they said, who was the messenger of peace and plenty. Hence, they proceeded that they must treat as spurious the revelation ascribed to the instrumentality of Gabriel. (Daryābādī, 1st ed., vol. 1 [Karachi: Dāru’l-Ishā‘at, 1991] p. 64)

1. The Jewish Encyclopaedia, 1st ed., vol. 5, [New York: KTAV Publishing House, 1901], p. 541

2. The Jewish Encyclopaedia, 1st ed., vol. 1, [New York: KTAV Publishing House, 1901], p. 593