This is not the only place in the Tanach where a prayer refers to HaShem as God of Abraham and Isaac – and after Jacob’s time such prayers add his name to the list, making the full phrase “God of Abraham, Isaac and Jacob”.
The question is why we need to mention the patriarchs at all. Why not simply begin with a straight-out personal call to the Almighty: “O my God…”?
The Baal Shem Tov explains why we need both descriptions of God when we pray – both “God of our fathers” and “our God”. He answers that there are two ways we find HaShem. We find Him in history and we find Him in our own personal experience, and we need both.
If He were only the God of our fathers, we would be relying too much on the tradition we have inherited from our ancestors and not making enough personal effort to encounter God for ourselves, in our own lives.
On the other hand, if we left our ancestors out of the reckoning and relied solely on our own spiritual efforts, we might be suffering from a delusion.
We need the perspective of the patriarchs as a corrective to what might be a personal illusion. We need the God of the past as well as the God of the present.
Maybe this is what Leo Baeck, the great German-Jewish thinker and leader, meant when he wrote: “Man lives not only in the circle of his years but also in the provinces of the generations from which he is descended.”