Midrash su Esodo 31:13

Raba b. Mechasia in the name of R. Chama b. Guria who spoke in the name of Rab said: "He who bestows a gift on his friend should let him know it; for it is said (Ex. 31, 13.) That ye may know that I am the Lord who doth sanctify you." We have also a Baraitha to the same effect: That ye may know that I am the Lord who doth sanctify you, i.e.. The Holy One, praised be He! said unto Moses "I have a good gift in my treasury; its name is Sabbath; this I wish to bestow on Israel; go, and announce it to them." "We learn from this then," said Rabban Simon b. Gamaliel, "that if one give a piece of bread to a child he ought to make it known to the child's mother." What shall one do [to inform the mother]? Abaye said: "He should put some oil around the child's eye or stain it with some dye" [so that his mother will ask him concerning it, and he will then tell her he also gave him bread]. Nowadays, however, when such is the apprehension of performing an act of witchcraft, what shall one do? R. Papa said: "He should put some of this very thing he gave to the child around his eyes." Is it so? [that a gift should first be told of]; has not R. Chama b. Chanina said: "He who bestows a gift on his friend should not let him know of it, for it is said (Ex. 34, 29.) And Moses did not know that the skin of his face shone, because He had spoken with him." This is not difficult to explain. The latter instance speaks of a thing that may become known by itself, but the former speaks of a thing that cannot become known by itself. Is not the Sabbath a thing that was to be known [and yet God informed Israel of it]? But the reward [for observing it] cannot be known.

R. Chisda held in his hand two priestly gifts from the meat of an ox and said: "I will give these to the man who will tell me one new law in the name of Rab." Whereupon Raba b. Mechasia said to him: "Thus, has said Rab, 'He who bestows a gift on his friend should inform him of it, for it is said (Ex. 31, 13.) That you may know that I am the Lord who doth sanctify you.'" So R. Chisda gave him the gifts. "Art thou so fond of the teachings of Rab?" asked Raba b. Mechasia. "Yea," he responded. Whereupon Raba b. Mechasia said: "This is what Rab said, 'Garments are precious to those who are invested with them, [because they know the value of it].'" "Did Rab indeed say so?" asked R. Chisda. "Surely the last thing is better than the first one, and if I had other gifts I would bestow them on you."

Observe the reward given for the observance of the Torah from the example of Pharaoh. Because Pharaoh said to Joseph, I am Pharaoh (Gen. 41:44), Joseph was exalted by him exceedingly, as it is said: And Pharaoh took off his signet ring and put it upon Joseph’s hand (ibid., v. 42). How much greater, then, is the reward bestowed by the Holy One, blessed be He, who with every commandment declares, I am the Lord (Exod. 31:13). (What else do we learn from this?) We learn from this that there is no limit to the reward given for the observance of the Torah. David foresaw this and declared: Oh how abundant is Thy goodness which Thou has laid up for them that fear Thee (Ps. 31:20).

Behold, Thou hast driven me out this day from the face of the land … and the Lord said unto him: “Therefore, whosoever slayeth Cain, vengeance shall be taken on him sevenfold.” and the Lord set a sign for Cain (Gen. 4:14–15). There are some who say that the word “Sabbath” was placed as a sign upon his countenance, as it is said: My Sabbaths, for it is the sign between Me and you, throughout your generations (Exod. 31:13), and that just as the Sabbath pleaded in behalf of Adam,³⁵The Sabbath pleaded with God to spare Adam’s life lest the glory and the sanctity of the Sabbath be impaired by his death. it pleaded in behalf of Cain. Others, however, insist that He fastened a horn upon his forehead.³⁶Bereshit Rabbah lists seven signs placed on Cain.

Rabbi Aḥa and Rabbi Tanḥum bar Rabbi Ḥiyya [said] in the name of Rabbi Yoḥanan: “Sanctify my Sabbaths” (Ezekiel 20:20) – in what way do you sanctify it? Sanctify it with food, with drink, and with clean garments, as it is written: “For it is a sign between Me and you, to know that I am the Lord…” (Exodus 31:13). “I am the Lord” – reliable to pay you a good reward.
Rabbi Ḥiyya bar Abba said: In the way of the world, a person performs labor with his employer, and because he sullies himself with mortar, [his employer] gives him his wages. However, the Holy One blessed be He is not so; rather, He says to Israel: ‘Do not sully yourselves with anything bad, and I will give you a good reward.’ That is what is written: “Do not make yourselves detestable” (Leviticus 11:43); “You shall not make a cut in your flesh for the dead…I am the Lord” (Leviticus 19:28). “I am the Lord” – reliable to pay you a good reward in the World to Come.

... The angels said before the Holy One, ‘Master of the World! Isn’t this Jerusalem?!’ as it is said “This is Jerusalem; in the midst of the nations I have placed her…” (Yechezkel 5:5) He replied to them, “But she exchanged My judgments for wickedness more than the nations…” (Yechezkel 5:6) They said to Him, “But they are Your people and Your inheritance, which You brought out with Your great strength…” (Devarim 9:29) He replied to them, “For My people have forgotten Me; they burn incense to vanity…” (Yirmiyahu 18:15) They said to Him, ‘act for the sake of the forefathers!’ He replied to them, “…the fathers are kindling fire…” (Yirmiyahu 7:18) They said to Him, ‘act for the sake of the children!’ He replied to them, “But they rebelled against Me and would not consent to hearken to Me…” (Yechezkel 20:8) They said to Him, ‘act for the sake of the tribe of Yehudah!’ “And Judah did what displeased the Lord…” (Melachim I 14:22) They said to Him, ‘act for the sake of the leaders!’ He replied to them, “Its heads judge for bribes…” (Micha 3:11) They said to Him, ‘act for the sake of the tribes!’ He replied to them, ‘and Gad, and Reuven and the half tribe of Menashe…’ They said to Him, ‘act for the sake of the tribe of Dan!’ He replied to them, “And the children of Dan set up for themselves the graven image.” (Shoftim 18:30) They said to Him,’ act for the sake of the students!’ He replied to them, “…And those who hold onto the Torah did not know Me…” (Yirmiyahu 2:8) They said to Him, ‘act for the sake of the prophets!’ He replied to them, “[It was] for the sins of her prophets, the iniquities of her priests…” (Eicha 4:13) They said to Him, ‘act for the sake of the kings!’ He replied to them, “And the altars that were on the roof, [the roof of] Ahaz's upper chamber, which the kings of Judah had made…” (Melachim II 23:12) The ministering angels said to Him, ‘act for our sake!’ He replied to them, “But they mocked the messengers of God…” (Divre HaYamim II 36:16) They said to Him, ‘act for the sake of Your name which is called upon them!’ He replied to them, ‘they have profaned My holy name.’ They said to Him, ‘You do not want to be appeased, what is the image of their father doing by You?’ “He has cast down from heaven to earth the glory of Israel…” (Eicha 2:1) This statement with which they clothed You, what has it done to You?! If the thing were not written, it would be impossible to say “The Lord has done what He devised, He has carried out His word…” (Eicha 2:17) They said to Him, ‘Master of the World! Is this not Jerusalem about whom you wrote “Behold on [My] hands have I engraved you…”’ (Yeshayahu 49:16) He replied to them, “I, too, shall clap My hands, one upon the other, and I shall put My fury to rest…” (Yechezkel 21:22) Since Zion saw that He did not want to be appeased, she started up and said “The Lord has forsaken me, and the Lord has forgotten me." (Yeshayahu 49:14) May it be Your will Lord our God and God of our fathers that Your Temple be rebuilt speedily in our days, that your Presence return within it, that You gather my exiles from the four corners of the world, that they rebuild the cities of Yehudah and settle Shechem and inherit it speedily. Amen.