One of the mitzvos on the Seder night is when we praise God; we begin with our disgraceful situations and end with our praiseworthy situations. There is a disagreement among the Rabbis as to what these situations are. According to Rav, we begin by telling that our forefathers in the time of Terach, Abraham’s father, were idol worshippers and end by saying that now God has brought us close to him, taught us the true ideas, and distinguished us from the rest of the nations. Shmuel says that we begin by saying that our forefathers were slaves in Egypt and all the evils that happened to us there, and we end by telling how God freed us with all the wondrous miracles. In our Haggadahs we do both.
I believe it is possible to explain the argument between Rav and Shmuel as follows: According to Rav, the essential praise we give to God Pesach night is the recognition of our ‘spiritual’ freedom. But according to Shmuel, it’s the recognition of our ‘physical’ freedom.