One of the implicit themes of Passover is the future “exodus” of the world from spiritual ignorance (a mistaken sense of separation from G-d) to universal spiritual awareness of G-d’s unchangeable presence in our lives.
In “Pesachim” — the tractate of the Talmud on Pesach – a prior mishnah that “One must bless G-d for the good and the bad”  becomes refined to: “In the future, we will only say the blessing “Ha-tov v’ha-meitiv”  — In the future, we’ll only bless G-d “for the good.” It means that in the future, we’ll recognize everything as being for the good. This is the higher and more accurate perception, as Rebbe Nachman of Breslav says: “Knowing that everything that has happened in life is for the good is a foretaste of the World-to-Come…” 
This doesn’t mean just a change in minhag (custom) or action. To truly see all as being for the good, our actual perception must change. We must always be seeing G-d in all. That, too, is a feature of the future:
Another prophet expresses the same promise:
The “Etz Hayim” chumash rightly associates this “light” with the Light created on the First Day – the revelation of G-d’s own Divine Light:
“Light…serves as a symbol of life, joy, justice and deliverance…Light, G-d’s first creation, becomes a symbol of G-d’s Presence, in the fire of the Burning Bush and the revelation at Sinai…” 
But G-d’s Light is far more than a “symbol.”
It’s an experience, often reported as an effect of prayer, meditation or contemplation.
What does it mean, then, to say, “At evening there will be light”?
The realization of G-d, or of G-d’s Presence, often includes the apperception of spiritual light. In meditation, this might be seen as “internal;” separate from created things. But in G-d Consciousness, this “internal” Light is seen along with created things. That is part of the meaning of “expanded consciousness”: our awareness expands to include both the material, changing world and at the same time, its unchanging spiritual source as well as the unchanging source of our own perception. Our eyes see the change from material light (day) to material darkness (night). Yet, we continue throughout both to see G-d’s Divine Light. Will this Light then still be seen as “separate from Creation? As permeating Creation? Not having had this experience clearly yet, I can’t describe it knowledgably. But the Light itself, and the apperception of it, is real – more real than the world.
A related verse from the same haftarah (prophetic reading) for Sukkot I, “On that day the L-rd will be One and His Name One,” was included in the “Aleinu,” a prayer originally said only on Rosh HaShanah. On the same day that we are told to recognize G-d as “King,” we are reminded that the entire creation will ultimately, inevitably do so, too.
Later, it was added to the services said every day, including all other holidays. Saying it at the end of each service, we reenter daily life on a note of cosmic hope.
So, we can appreciate the liberation of the B’nai Yisrael from Egypt as the beginning of a process of liberation from fear, hatred, ignorance, sadness and pain that has not yet reached its climax: Universal awareness of the Light and Joy of G-d.
There really can be no greater liberation than this. We need economic and social justice, but they, too, will never be complete until each of us is free within ourselves.
The “Cup of Elijah” that concludes the seder is really only the beginning of a wonderful future.
Hag Pesach Sameach v’Kasherl