Gabriel is one of only two angels named in the Hebrew Bible, and the errand is always the same. He arrives to say what is going to happen.
Daniel
He appears in the book of Daniel, sent to explain the vision of the ram and the goat and later the seventy weeks. He is described as having the appearance of a man, and Daniel is terrified of him. Nothing in the text calls him an archangel.
Luke
In the gospel of Luke he appears twice in the opening chapter. He tells the priest Zechariah in the sanctuary that his wife Elizabeth will bear a son, and strikes him mute for doubting it. Six months later he is sent to Nazareth to tell Mary that she will bear Jesus. The second of these scenes, the Annunciation, is among the most painted moments in European art, which is why most people picturing Gabriel are in fact picturing Luke chapter 1.
The Quran
In the Quran he is Jibril, named in sura 2 and again in sura 66, in both places in a setting of support and revelation. Islamic tradition holds that he is the angel who conveyed the Quran to Muhammad across some twenty-three years, and most commentators identify him with the Trustworthy Spirit and the Holy Spirit named elsewhere in the text.
The same errand
Three scriptures, three languages, and roughly a thousand years between the first and the last, and in each of them Gabriel does one thing. He delivers something the hearer did not ask for and cannot refuse. He is never worshipped, never a god, and never acts on his own account.