Frank Moore Cross’s model of covenant as an early legal means of extending fictive kinship has dominated Anglo-American biblical scholarship for the last thirty years. His central case study is the covenant between David and Jonathan and the associated oath sworn by Jonathan in 1 Sam 20. In trying to distill a simple covenant concept, however, Cross collapses distinctions of genre and context, reducing the significance of secular covenant as a form of political bond to simply merging kinship groups. In this article, I reanalyze the oath in 1 Sam 20:12–17, contextualizing it with other material throughout 1 and 2 Samuel and comparing it to ancient Near Eastern treaty formulations to show its political significance in Israelite history. In contrast to Cross’s notion of imposing kinship obligations, the oath addresses questions of succession and dynasty, anticipating the political turmoil of David’s ascension to the throne. Deuteronomistic language and concern with Davidic succession shared between the oath and the divine promise in 2 Sam 7 point to a common vision of a united kingship. Far from the reiteration of a simple kinship bond, Jonathan’s oath of loyalty to their covenant becomes a keystone in the Deuteronomistic ideal of an eternal Davidic dynasty.