מדרש אויף דברים 2:31

“The Lord said to me: See, I have begun delivering before you Siḥon and his land; begin taking possession of his land” (Deuteronomy 2:31).
“The Lord said to me: See, I have begun…” – halakha: If a person of Israel is walking on the road on the day before Shabbat and it begins getting dark, and he has money or something else in his hand, what must he do? So taught the Sages: One for whom it became dark [while he was traveling] on the road gives his purse to a gentile. Why is it permitted for him to give it to a gentile? Rabbi Levi said: When the descendants of Noah were commanded, they were commanded regarding only seven matters, and Shabbat is not one of them. That is why they permitted him to give it to a gentile.
Rabbi Yosei bar Ḥanina said: An idolater who observed Shabbat before he accepted circumcision upon himself incurs liability to be put to death. Why? Because they were not commanded [to observe] it. What did you see that led you to say that an idolater who observed Shabbat incurs liability to be put to death? Rabbi Hiyya bar Abba said that Rabbbi Yoḥanan said: The way of the world is that when a king and a noblewoman are sitting and conversing with one another, one who comes and inserts himself between them, does he not incur liability to be put to death? So, the Shabbat is between Israel and the Holy One blessed be He, as it is stated: “Between Me and the children of Israel [it is a sign forever]” (Exodus 31:17). That is why any idolater who comes and inserts himself between them, before he accepted circumcision upon himself, incurs liability to be put to death. The Rabbis say: Moses said before the Holy One blessed be He: ‘Master of the universe, given that idolaters were not commanded regarding Shabbat, if they observe it, will You lift Your countenance to them?’ The Holy One blessed be He said to him: ‘Do you fear this matter, as you live, even were they to fulfill all the mitzvot in the Torah, I will topple them before you.’ From where is this derived? From what we read regarding the matter: “See, I have begun delivering before you.”

Another matter, “see, I have begun” – this is what the verse said: “To bind their kings with fetters” (Psalms 149:8). Who are “their kings”? These are the kings of the idolaters. “And their nobles with iron chains” (Psalms 149:8) – these are their guardian angels on High, as the Holy One blessed be He does not exact retribution from a nation until He first exacts retribution from its guardian angel. How so? The Holy One blessed be He did not submerge Pharaoh and all the Egyptians in the sea until He first submerged its guardian angel. From where do we derive this? The Rabbis said: “Horses and their riders” is not written here, but rather, “the horse and its rider” (Exodus 15:1) – this is their guardian angel. When the Egyptians departed to pursue Israel, Israel lifted their eyes and they saw Egypt’s guardian angel floating in the air. From where is this derived? Rabbi Yitzḥak said: As it is written: “Behold, Egypt was traveling after them” (Exodus 14:10) – this is their guardian angel. That is, “to bind their kings with fetters…” (Psalms 149:8). Siḥon and Og, too, when they sought to confront Israel, the Holy One blessed be He said to Moses: ‘See that I have toppled their guardian angel, as it is stated: “See, I have begun delivering before you.”’

Another matter, “see, I have begun” – this is what the verse said: “Expectation deferred sickens the heart” (Proverbs 13:12). Rabbi Azarya said: It is speaking of the salvation that is expected to come. How so? When the prophet says to Israel: “Another one will be soon, and I will quake the heavens, and the earth” (Haggai 2:6), they say: “Expectation deferred sickens the heart.” When he said to them: “Behold, your Savior has come” (Isaiah 62:11), they said: “And desire realized is a tree of life” (Proverbs 13:12).
Another matter, “expectation deferred” – this is Pharaoh, as Moses was coming and going and bringing plagues upon him, and with each and every plague, Israel believed that he would release them. “And desire realized is a tree of life” – this is the wars of Siḥon and Og, as the Holy One blessed be He said to him immediately: “See, I have begun delivering before you.”
Another matter, what is “see, I have begun”? The Holy One blessed be He said to Moses: ‘Moses, see that I have toppled their guardian angel.’ Rabbi Abba bar Kahana said: Like a king who ties up his son’s enemy, and says to him: ‘Do to him anything that you wish.’