Deuteronomy 4:41

And now, behold, Mosheh set apart three cities beyond the Jordan toward the sunrise,

At that time Moshe set aside… The day Moshe announced the Covenant coincided with the day he set aside these three cities.

THEN MOSES SEPARATED THREE CITIES. Rabbi Abraham ibn Ezra explained it to mean: “on the day that Moses separated three cities [to function as cities of refuge], he then said the words of the covenant [as stated in the following section].” But it is not correct. Rather, it is to be understood in its simple sense. Moses had gathered all Israel to explain to them the Torah and he began with words of reproof; after he uttered in their presence his words of reproof concerning what they had done, the admonishments about idolatry and the Unity of G-d, and completed [his statement] to them with the charge that they observe His statutes and His commandments so that it may be well with them — then he said in their presence before them: “Now we shall fulfill the commandment that G-d has commanded us, and Bezer in the wilderness, Ramoth in Gilead, and Golan in Bashan will be cities of refuge that every manslayer that kills any person through error may flee thither.” And although they would not legally provide refuge until [the cities of refuge] in the land of Canaan [on the western side of the Jordan] were set apart, Moses said, “‘If a commandment has come to our hands we shall fulfill it,’ so that it may be well with us.” Afterwards he called with a great voice to all Israel that were there and said to them, Hear, O Israel, the statutes and the ordinances etc., for now he commenced to speak of the commandments and the explanation of the Torah, as I have explained at the beginning of the section These are the words.

אז יבדיל משה, Why did the Torah interrupt Moses’ speech which were coherent, sequential and continuous, and it now introduced another subject in the form of a narrative? Actually, Moses had dwelled at length on the past and the time had come to do what the Torah had said at the outset, i.e. to elaborate on aspects of the Torah on which Moses had either not elaborated previously, or had not presented to the people at all, or felt that it was essential to repeat the legislation in question to prevent problems after he was no longer on the scene to deal with them.
The subject of the cities of refuge is of concern to the judges and the whole system of the judiciary introduced by Moses as the first subject of legislation which he reviews. Already in chapter one, Moses addressed primarily the judges on whom rests the responsibility of ensuring a functioning government. In chapter 19,2 the Torah commands the setting aside of 3 such cities of refuge each on the west bank and on the east bank of Jordan (verse 9). Since it did not mention the three cities Moses had already established on the east bank of the Jordan this had to be added here, to show that the numbers given in the Torah are flexible, i.e. that as the territory of the Jewish people expands the need to add more such cities may arise. The command issued in Numbers 35,14 was not to be effective immediately as the Israelites had not yet crossed the Jordan. Moses had nonetheless set aside such cities although they did not yet function as such.

אז יבדיל משה שלש ערים, after he had concluded with his introduction to the detailed discourse on the Torah. The reason why he set aside these cities at that time was to show the Israelites how the observance and carrying out of G’d’s commandments is of such supreme importance, and that he, though about to depart the earth, wanted to perform at least this commandment, the observance of which is linked to the land of Israel.

אז יבדיל משה שלש ערים, “then Moses set aside three cities, etc;” the expression אז is usually reserved as introduction to a poem, a song; compare Exodus 15,1, so that its appearance here is somewhat puzzling. When the people had heard the legislation about the cities of refuge in Numbers 35,33, where the Torah decreed that blood spilled of a person who was innocent could never be atoned for by a payment of ransom, they were afraid that even if someone were to commit a killing unintentionally he would be subject to the death penalty; Moses reassured them that there was another method by which such a person could atone for his negligence in having caused the death of an innocent person, i.e. his being forced to reside in a city of refuge until the death of the High Priest at that time. When they heard this they broke out in a song of relief. This was remindful of the proverb that (only) if someone has tasted a dish does he really know what it tastes like. Moses, who had had cursed an Egyptian who had slain a Jew by using the holy name of the Lord, had been forced to flee and reside outside his homeland for close to 60 years. He therefore understood that this was a very harsh penalty. [Our author clearly belongs to the school of thought that does not consider Moses as a hero for taking the law into his own hands. Ed.]

מזרחה שמש, “on the east side facing the sun” All the murderers listed in the Bible fled eastward. Adam, whose penalty for eating from the tree of knowledge was supposed to be death, fled in that direction, seeing that he had caused the mortality of every human being. (Compare Genesis 3,24, “he took up residence east of gan eden). Kayin who had murdered his brother) settled also in the east as we know from Genesis 4,16.