“What is light? Rav Huna said, ‘light,’ and Rav Yehuda said ‘night’” (Rish Pesachim).
“Jacob went out from Beer Sheba and went to Haran and arrived at the place.” “Jacob went out,” The Zohar says, from Beer Sheba, from the land of Israel. “Went to Haran,” abroad. Our sages said that Abraham and Isaac established the morning and afternoon prayers, which are mandatory, and Jacob established the evening prayer, which is optional (Berachot 26b).
We should understand why the prayer of Jacob—who is the senior among the patriarchs, and who is called “Jacob, a complete man,” eliciting twelve tribes—is not mandatory like the prayers of Abraham and Isaac.
Normally, one who feels that his friend is doing him a favor feels a moral debt to bless him for the favor that he did for him and will return him favors henceforth.
But one who does not feel that his friend did him a favor, but thinks that perhaps he did him favors, he does not feel he should be grateful and that he should seek something from him. Rather, he has an option. In other words, the body does not feel indebted to ask of the other one, but this is an option, and he has the choice whether or not to do so. But if he feels that his friend has given to him, the body feels a debt to his friend.
Jacob, the complete man, wanted to correct the wholeness of the generations and the times and states. This is the difference between day and evening, since “day” is when he feels good and his heart is glad. That state is called “day.” If it is to the contrary, he says, “the world has grown dark on me.”
“Jacob went out from Beer Sheba,” which is the land of Israel, a Be’er [well] from which water is pumped, when a person feels satiated and that he does not lack a thing, “and went to Haran,” to a place where there is no satiation and there is Haron Af [anger/wrath]. This is called “evening.” At that time, the body is not obliged to thank his friend and ask something of his friend. On the contrary, he has grievances against his friend.
“And he came to the place.” This is a correction, for even in a place that is the evening prayer, when prayer is optional, meaning a choice, he should overcome and pray. But the body does not feel any obligation while it is dark for it.
Hence, Jacob, the senior among the patriarchs, established wholeness for the general public, so they can pray the evening prayer, at which time it is optional.
A person should make a choice so that the body will want to pray, since at that time it does not feel any obligation, as it is evening and not day. When it feels the state of “day,” the body feels obliged. Through the optional prayer, which is evening, we come to a “day,” and then it is a mandatory prayer.
Likewise, the blessing [grace] for the food is mandatory at a meal where there is satiation, as it is written, “And you shall eat, and be satisfied, and bless,” to imply the above-mentioned, that when the body feels the state of “Beer Sheba,” when it is Save’a [satiated], the body feels obliged to pray. But when he feels the state of “evening,” the prayer is optional to the body and he needs the work of choice so he can pray.
By this we can interpret the dispute over the interpretation of “light to the fourteenth” [the night before the 14th of the month] when we examine the leaven. The Gemara asks, “What is light?” Rav Huna says, “light is light,” and Rav Yehuda says, “Light is night.” We should understand how come they are disputed. From the perspective of the Kli [vessel], being rewarded with the light requires that we first feel the darkness. Hence, light is mainly “night.” When we speak from the perspective of the abundance, not from the perspective of the Kli, the abundance is called “light,” which is day.
This is the meaning of “The voice is the voice of Jacob, and the hands are the hands of Esau.” The body is regarded as the quality of Esau, since as soon as one is born, the evil inclination comes to him. Hence, it is regarded as Esau: It is complete and knows what is good and what is bad.
When the good inclination comes to him and tells him that there is a different good than what he knows to be considered good, he does not want to listen. The good inclination tells him, “The wicked in their lives are called ‘dead.’” But he does not understand what it is telling him; he thinks that it is the complete opposite.
It was said about this, “The voice is the voice of Jacob, and the hands are the hands of Esau,” meaning that through the voice of Jacob, which is the evening prayer, the Kelim [vessels] of Esau can receive correction, and the darkness will be turned to day, as it is written, “And it came to pass that when evening falls, it will become day.”