Albert Barnes Commentary Luke 1:55

"(As he spake unto our fathers) Toward Abraham and his seed for ever." — Luke 1:55 (ASV)

As he spoke to our fathers. This means he has dealt mercifully with the children of Israel, as he promised Abraham, Isaac, and Jacob. The promise particularly referred to here is that concerning the Messiah, which was now about to be fulfilled. However, there is no doubt that also included were the promises concerning all the other mercies that had been bestowed upon the children of Israel. See Genesis 22:17-18.

For ever. These words refer to the preceding verse—in remembrance of his mercy for ever, to Abraham and to his seed for ever.