When considering the rhetorical structure of the Sermon on the Mount, Hans Dieter Betz has noted that, “There clearly appears to be rationale behind the six antitheses and their arrangement in the [Sermon on the Mount], but that rationale has so far eluded scholarship; few scholars have even discussed the question” (Betz, The Sermon on the Mount, 201). In this paper I address Betz’s question by identifying two parallel sources that similarly juxtapose materials underlying the last three antitheses, suggesting that the combination found in Matthew draws upon a related tradition.  Building upon earlier research where I demonstrate that the fifth and sixth antitheses reflect a Second Temple Period interpretation of Lev. 19:17-18, in the present paper I demonstrate how Jewish sources often discuss these two biblical verses in tandem with the topic of oaths (the focus on the fourth antithesis).  Examining passages from the Damascus Document and the Testament of Gad, I show how each of these sources connects the theme of oaths to a discussion of Lev. 19:17-18.  Although Matthew and these two Second Temple period texts employ divergent rationales for linking a discussion of Lev. 19:17-18 and oaths, the presence of a connection between them speaks to a shared tradition that may have informed the order and organization of the Matthean antitheses.  In addition to advancing our understanding of the thematic organization of the Sermon on the Mount, this paper also argues for a broader mode of textual comparison between Jewish and Christian texts from Late Antiquity by looking to larger thematic structures rather than individual pericopae.