When scholars of early Judaism and Christianity identify a writing as an “apocalypse” (in terms of genre), they usually have in mind a first-person visionary report that claims to narrate a “revelation” (apocalypsis) from God himself. Almost always the content of the visions that are narrated also presuppose or directly pertain to an apocalyptic worldview, namely, an ideology in which this present world is dominated by evil forces (headed by Satan, or Beliar, or what have you) which will ultimately and imminently be destroyed (or perpetually punished) in the final intervention of God and his angelic forces (there is a thoroughgoing dualism in this way of thinking).
One of the two main types of apocalyptic writing that have been identified is the so-called “historical apocalypse”. Here the focus of the visions relates to the unfolding of God’s historical plans (on this, see John J. Collins, The Apocalyptic Imagination, which is browsable online here). The Book of Daniel in the Hebrew Bible (written about 160s BCE) and John’s Apocalypse or Revelation (written about 70-90 CE) in the New Testament are largely characterized by this historical focus: both relate the unfolding of God’s plan for history in relation to actual political powers (Hellenistic kings and Roman emperors, respectively), and these political powers are cast in the role of the ultimate evil opponents of God (on John’s Apocalypse see my earlier post on Worshiping the Beast / Honouring the Emperor or my article here).
The second main type of apocalypse is the “otherworldly journey”. Here the visionary is taken on a tour of the far reaches of the world and beyond, usually a tour of either the heavens or the underworld (hell). The earliest surviving example of this type is the first book (chs. 1-36) of 1 Enoch (online here) written about 200 BCE, in which the Enoch of Genesis is presented as the visionary who expounds the story of the fallen angels (Gen 6) and is guided by an angel in order to witness the workings of the universe.
In its present Christian form, the Ascension of Isaiah (reflecting materials ranging from the second century BCE to as late as the fourth century CE; online here) consists of the story of the prophet Isaiah’s martyrdom (who is sawn in half) and a report of Isaiah’s vision in which Isaiah is taken on a journey through the seven heavens with an angel as guide (chs. 1-5 and 6-11 respectively). The martyrdom and the vision are linked in their present form, since it is because Isaiah had gone on the tour, witnessing God’s plan to send his Beloved (Christ) to destroy the evil powers, that Beliar (Satan) seeks to have Isaiah killed (through the evil angel Sammael and king Mannaseh) (3:13).
Isaiah’s otherworldly journey begins as he ascends with the angel-guide to “the firmament” above the world, but below the heavens. Isaiah then proceeds through each of the seven heavens. In each heaven he witnesses a throne flanked by angels, and the glory of each heaven and its angels increases until he reaches the final, seventh heaven, the dwelling place of the Most High (God) and his “Beloved” (Lord Christ). There, says Isaiah,
“I saw all the righteous from Adam. And I saw there the holy Abel and all the righteous. And there I saw Enoch and all who were with him, stripped of the garment of the flesh, and I saw them in their higher garments, and they were like the angels who stand there in great glory” (Ascension of Isaiah 9:7-9; trans. by Müller in Schneemelcher)
Isaiah then gains a revelation of what will occur in the future, final intervention of God (the end times). Ascending and descending are important not only for Isaiah here, but also for other key figures in the apocalyptic visions. Isaiah hears the voice of the Most High himself calling on his Beloved (Lord Christ) to descend, to trace the steps that Isaiah had just traversed, in other words:
“Go and descend through all the heavens; descend to the firmament and to that world, even to the angel in the realm of the dead (on the descent to hell see my other posts on Satan) . . . that you may judge and destroy the prince and his angels and the gods of this world and the world which is ruled by them, for they have denied me and said ‘We alone are, and there is none beside us’. And afterwards you will ascend from the angels of death to your place, and you will not be transformed in each heaven [i.e. you will not be affected by the inferiority of each heaven in relation to the seventh heaven], but in glory you will ascend and sit on my right hand. And the princes and powers of this world will worship you” (Ascension of Isaiah 10.7-14).
Almost immediately, Isaiah then witnesses the descent and ascent of the Beloved (Christ). But there is more of this ascending and descending. Earlier in this writing we learn that, as part of the “consummation” of the world, an anti-Beloved (so to speak), Beliar himself, will be sent before the Beloved comes:
“And after it has come to its consummation, Beliar, the great prince, the king of this world who has ruled it since it came into being, shall descend; he will come down from his firmament in the form of a man, a lawless king, a slayer of his mother, who . . . will persecute the plant which the Twelve Apostles of the Beloved have planted; and one of the twelve will be delivered into his hand. . . All that he desires he will do in the world; he will act and speak in the name of the Beloved and say ‘I am God and before me there has been none else’. And all the people in the world will believe in him, and will sacrifice to him and serve him saying, ‘This is God and beside him there is none other’ . . . And after (one thousand) three hundred and thirty-two days the Lord will come with his angels and with the hosts of the saints from the seventh heaven with the glory of the seventh heaven, and will drag Beliar with his hosts into Gehenna” (4:1-14).
In a manner reminiscent of John’s Apocalypse (esp. ch. 13), the author is here presenting an end-time evil figure in the form of an actual king and, more specifically, a king modelled on a returning emperor Nero (Nero redivivus) who is worshipped as a god (alluding to the Roman imperial cult, on which go here for a brief discussion or here for an entire article). It is important to remember that the line between “otherworldly journey” apocalypses and “historical” apocalypses is by no means stark (as with the fluidity of genre as a whole), and there are some apocalypses with the characteristics of each, of course.
The ascending and descending theme is an important component in this apocalyptic author’s worldview, and the apocalyptic seer’s own guided tour gives him a first-hand experience of otherworldly travel himself.
UPDATE (Dec. 15): Now also see Alan S. Bandy’s collection of various scholarly definitions of the apocalyptic genre.