“God has remembered
That he swore
To our ancestor
ὅρκον ὃν ὤμοσεν πρὸς Ἀβραὰμ τὸν πατέρα ἡμῶν, τοῦ δοῦναι ἡμῖν
In case there was any doubt about what covenant or agreement Zechariah was talking about, he made it clear, via this canticle in Luke, that this was the covenant or agreement with Abraham to have him and his many descendants be prosperous as in Genesis, chapter 22:16-18. Zechariah said that God had remembered or given them (τοῦ δοῦναι ἡμῖν) the oath (ὅρκον) that he swore (ὃν ὤμοσεν) to Abraham (πρὸς Ἀβραὰμ), their ancestor or father (τὸν πατέρα ἡμῶν). The covenant was coming about right before their very eyes. Notice it was not the Mosaic, but the older Abrahamic covenant that Luke emphasized.