Jibril has been entitled Ruh Al-Qudus for bringing down the miracle of Qur'an. He is one of the messengers of Allah, and the only one who interacted with human beings i.e. Prophets. Refuting one messenger equals refuting all. Besides Jibril this is true of all Prophets as well. If one rejects Prophet Isa (Jesus) then he has rejected all prophets, if one rejects prophet Musa (Moses), or Haroon (Aaron), or Yaqub (Jacob), any from the chain of prophets beginning from prophet Adam, he will be considered equal to have refuted the entire chain. Muslims believe in the complete chain right to the very conclusion, the seal of Prophethood at Prophet Muhammad sal allahu aleyhi wa a'aleyhi wasallam. Believing in Ruh Al-Qudus i.e. Jibril; therefore, is a critical component of belief because he is the link between Allah and the prophets, the medium of communication between them.
Ruh Al-Qudus means the Trustworthy Spirit. Jibril's missions to descend with the Word of Allah were conducted on Allah's Command and not of his own will. Allah's Messengers; therefore, are both angels and men and all of them should be acknowledged by the Believers unless they wish to invoke Allah's fury. Mika'il also descended with Allah's Message to some prophets, which is why the Jews considered him a friend, but his real work is to make winds and weather by Allah's Command. The work of carrying out Allah's revelation to the prophets is basically Jibr'il's. In the Qur'an, Allah has mentioned Jibr'il and Mika'il together to highlight the equal importance of Jibr'il and Mika'il and the rejection of one causes the rejection of the other.
By refusing to believe in Jibr'il; therefore, it is clear that one invokes the fury of Allah.
References
Tafsir Ibn Kathir, Vol. 1, p.304-306, Darussalam Publications
