Marvin Sweeney's essay on form criticism provides an interesting perspective on Genesis 15 and specifically, the various forms or genres present in the chapter depicting Abraham as a prophet, priest, and king. Looking at the literary markers in the chapter and the "comparative identification of typical language forms in the text that appear elsewhere in biblical and ancient Near Eastern literature," certain genres can be discerned which aide in the interpretation (or exegesis) of the text. Sweeney cautions, however, that attempts to "reconstruct genres are constrained by the limited surviving textual base for ancient Near Eastern cultures." Accordingly, the form-critical hermeneutic isn't entirely definitive, however, sufficient evidence within the text and the ancient Near East provides for a high degree of reliable interpretation.
A discussion of certain "generic forms" that "function within the narrative context," are highlighted below:
The first is the formula "the word of YHWH was unto Abram, saying . . ." in verse 1. This formula is known technically as the Prophetic Word Formula. It appears frequently in narrative and prophetic literature as a typical means of introducing and identifying a prophetic word or oracle. . . .The presence of this formula in Genesis 15 is particularly striking in that it presents Abram as a prophet or at least an individual who experiences a prophetic vision. This, of course, ties to the notice that Abram experiences the word of YHWH "in a vision" (v. 1).
[Another] generic form in Genesis 15 involves the self-identification formula in verse 7, "I am YHWH who brought you out from Ur of the Chaldees to give to you this land to possess it". . . .the self-identification formula also relates to language pertaining to a fifth genre in Genesis 15. The expression in verse 18 reads literally, "On that day, YHWH cut with Abram a covenant." The expression "to cut a covenant" is a standard idiomatic form for expressing the making of a treaty in ancient Israel and the Near East. The expression derives from the practice of sacrificing animals as part of the process of ratifying a treaty between two nations. Parties to a treaty walked between the halves of severed animals as a graphic portrayal of what would happen to them if they did not abide by the terms of the treaty. . . .This practice apparently stands behind YHWH's instructions to Abram to cut several sacrificial animals in half so that YHWH, represented by the smoking fire pot and flaming torch can pass between the pieces. In effect, YHWH "signs" or "affirms" the treaty, which validates YHWH's promises. . . .Abram is portrayed vaguely in priestly terms here, insofar as he receives oracular communication and prepares the sacrificial animals for the making of a treaty. . ."
There are royal connotations in Abram's presentation, however, that must be considered. Throughout the Genesis narrative, Abram is closely associated with the city of Hebron - indeed he is buried there - a city that served as the capital of the tribe of Judah and the seat of David's first kingdom (2 Samuel 2-5). Abram acts in a manner analogous to that of a king. He walks the length of his land founds cultic sites (Genesis 12), allocates land to family members (Genesis 13), goes to war to protect them (Genesis 14), decides the fate of family members under his authority (Genesis 16; 21), stands up even to YHWH in order to maintain justice within his sphere (Genesis 18), arranges a marriage for his son with a foreign principal (Genesis 24), and enters into covenants (Genesis 15; 17). The language pertaining to covenant making likewise points to a royal setting. As noted in the previous discussion of genre, the assignment of land, the ritual of passing through the pieces of slain animals, and YHWH's self-identification formula all derive from the sphere of ancient Near Eastern treaty making. The social setting, then, is that of international relations in the ancient world, and this again points to the monarchy as the principal party involved in the making of such treaties. Indeed, the most telling aspect of Abram's royal presentation is the definition of the land YHWH promises him as "this land from the River of Egypt to the great River, the River Euphrates," for this is also the definition of the land claimed for David in 2 Samuel 8 (cf. Numbers 34; Ezek. 47:13-20). The royal context is confirmed by the portrayal of the land as Abram's "reward," or spoil of war, and by the assignment of the land to Abram's "seed," a designation that also appears int he language of YHWH's promise to David of an eternal dynasty. . . .Genesis 15 portrays Abram in Davidic terms as the founder of a dynasty that will possess a land."
Marvin A. Sweeney, "Form-Criticism," To Each Its Own Meaning: An Introduction to Biblical Criticisms and Their Applications, eds. Steven L. McKenzie and Stephen R. Haynes (Louisville, KY: Westminster John Knox Press, 1999), 75-80