Luke 1:72

Luke 1:72. To show mercy toward our fathers. The word ‘promised' was supplied in the E. V., because of the difficulty involved in the thought of showing mercy to those already dead. But the expression is poetic. The pious Jews of old had wept over the decay of their nation, and even though dead and living with God, the fulfilment of their hopes and wishes might be called showing mercy toward them.

And to remember his holy covenant , i.e., by the act of fulfilling what He had promised therein to show His mindfulness of it.