All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
The Injeel was revealed just as the Quran and Torah were revealed through the angel Jibreel . Allaah Says (which means): {And We gave Jesus, the son of Mary, clear proofs, and We supported him with the pure spirit (i.e., Jibreel).}[Quran 2:253]
The Muslim scholars have clearly mentioned that Jibreel was the mediator between Allaah and His messengers, may Allaah exalt their mention. The scholars also mentioned in their books that the Torah and the Injeel, were revealed all at once not in separate portions. Imaam Al-Qurtubi wrote in the explanation of the verse (which means): {And those who disbelieve say, “Why was the Quran not revealed to him all at once?”}[Quran 25:32] He said: 'They (disbeliever) enquired why He (Allaah) did not reveal the Quran on the Prophet at once as the Torah was revealed on Moosaa, Injeel was revealed on 'Eesaa, and Psalter was revealed on Daawood, may Allaah exalt their mention.' Imaam Ibn Katheer said: '… as the divine Books were revealed at once before the Quran.'
Therefore, the Injeel was revealed on 'Eesaa by Jibreel at once, may Allaah exalt their mention, not like the Quran which is revealed gradually throughout the period of twenty three years.
These are the general facts that were related about how the Books were sent down, and we do not know the other details.
Finally, we advise the brother to seek the knowledge of the matters that help doing good deeds not the knowledge that does not improve your deeds.
Allaah Knows best.