In common with other apocalyptic writings, such as Daniel and 1 Enoch, John’s letter employs vivid, memorable imagery. As with the other elements of his Apocalypse (Revelation), John draws on existing sources for his material.
Meanings inferred from the images need to keep the following firmly in mind:
1. The symbols had to have meaning for and be clearly understood by his immediate intended hearers.
2. John intended that these images encourage those hearers to “overcome”, then and there.
3. John anticipated that the Coming of Jesus was imminent, “soon”.
It is my belief that the images were intended to depict earthly opposition (Rome and apostate Jews) as well as heavenly opposition (wars in heaven involving Satan).
The writers/compilers of Daniel also employed vivid imagery. They wrote while their community was under threat by Antiochus Epiphanes. Through the use of vivid images, John and Daniel were able to pass on supportive messages to their respective communities.
For his symbols, John made full use of the array of material available to him. There was no Canon of Scripture at the time.
The following citations on the imagery of the seven-headed beast provide Jewish and non-Jewish sources available to John.
Common to both Yahweh and Baal was also a constellation of motifs surrounding their martial and meteorological natures. The best-known and oldest of these motifs is perhaps the defeat of cosmic foes who are variously termed Leviathan, ‘qltn, tnn, the seven-headed beast, Yamm, and Mot. (The Early History of God: Yahweh and the Other Deities in Ancient Israel, page 85, Mark Smith).
A seal from Tel Asmar (ca. 2200) depicts a god battling a seven-headed dragon, a foe identified as Baal’s enemy in CTA 5.1 (KTU 1.5 I).3 (and reconstructed in 30) and Yahweh’s adversary in Psalm 74:13 and Revelation 13:1. A shell plaque of unknown provenance depicts a god kneeling before a fiery seven-headed dragon. Leviathan, Baal’s enemy mentioned in CTA 5.1 (KTU 1.5 I).1 (and reconstructed in 28), appears as Yahweh’s opponent and creature in Isaiah 27:1, Job 3:8, 26:13, 40:25 (E 41:1), Psalm 104:26, and 2 Esdras 6:49, 52. In Psalm 74:13-14 (cf. Ezek. 32:2), both Leviathan and the tannînîm have multiple heads, the latter known as Anat’s enemy in 1.83.9-10 and in a list of cosmic foes in CTA 3.3(D).35-39 (= KTU 1.3 III 38-42). This Ugaritic list includes “Sea,” Yamm//“River,” Nahar, Baal’s great enemy in CTA 2.4 (KTU 1.2 IV). In Isaiah 11:15 the traditions of Sea//River and the seven-headed dragon appear in conflated form:
And the Yahweh will utterly destroy the tongue of the sea of Egypt, and will wave his hand over the River with his scorching wind, and smite it into seven channels that men may cross dry-shod.
Here the destruction of Egypt combines both mythic motifs with the ancient tradition of crossing the Red Sea in Egypt. The seven-headed figure is attested in other biblical passages. In Psalm 89:10 the seven-headed figure is Rahab, mentioned in Isaiah 51:9-11 in the company of tannîn and Yamm. The seven-headed enemy also appears in Revelation 12:3, 13:1, 17:3 and in extrabiblical material, including Qiddushin 29b, Odes of Solomon 22:5, and Pistis Sophia 66. Yamm appears in late apocalyptic writing as the source of the destructive beasts symbolizing successive empires (Dan. 7:3). J. Day has suggested that this imagery developed from the symbolization of political states hostile to Israel as beasts. (The Early History of God: Yahweh and the Other Deities in Ancient Israel, pages 86-87, Mark Smith).