This article isolates three parallels to the expression, ‘he spoke… forever’ (Luke 1,55) in translations of the Psalms of Solomon and Jubilees. These parallels suggest that Luke 1,55 calques a Hebrew idiom for oath-swearing, likely known to Luke from Greek translations in his sources. Read in light of these parallels, Luke 1,55 fulfills a crucial structural and rhetorical function in its climactic position in the Magnificat, reinforcing the unity of the hymn’s second strophe (vv. 50-55), and giving shape to its theology of covenant and salvation.