Emor: Why Do We Have Rosh Hashanah?

(24) Speak to the Israelite people thus: In the seventh month, on the first day of the month, shall be for you a [day of] rest. A remembrance of the sounding [of the shofar], a holy assembly.

(1) זכרון תרועה [THERE SHALL BE UNTO YOU] A REMEMBERANCE זכרון OF SOUNDING THE SHOFAR — (זכרון) the Divine remembrance and Biblical verses which have reference to the blowing of the Shofar (a ram’s horn) on the occasion of important historical events that I may recall to memory (זכרון) for you the offering, or binding, of Isaac in whose stead a ram was offered, having been caught by its horn (שופר‎).

(1)“Speak to the children of Israel, saying: In the seventh month, on the first of the month, shall be a rest for you, a remembrance by means of a blast, a holy convocation” (Leviticus 23:24). “In the seventh month, on the first of the month” – that is what is written: “Forever, Lord, Your word stands in the heavens” (Psalms 119:89). It is taught in the name of Rabbi Eliezer: On the twenty-fifth of Elul, the world was created...On the day of Rosh HaShana, in the first hour it entered His thoughts, in the second [hour] He consulted with the ministering angels, in the third He gathered his dust, in the fourth He kneaded it, in the fifth He shaped it, in the sixth He made it into a lifeless body, in the seventh He breathed a soul into him, in the eighth He brought him into the Garden, in the ninth he was commanded, in the tenth he transgressed, in the eleventh he was sentenced, in the twelfth he emerged with a pardon. The Holy One blessed be He said to Adam: ‘This is a portent for your descendants. Just as you stood trial before Me this day and emerged with a pardon, so your descendants are destined to stand trial before Me on this day and emerge before Me with a pardon.’ When? It is “in the seventh month, on the first of the month.”

(1)They are four days in the year that serve as the New Year, each for a different purpose: On the first of Nisan is the New Year for kingsandfor the order of the Festivals.On the first of Elul is the New Year for animal tithes;Rabbi Elazar and Rabbi Shimon say: The New Year for animal tithes is on the first of Tishrei.On the first of Tishrei is the New Year for counting years,for calculating Sabbatical Years and Jubilee Years,for planting,and for tithing vegetables.On the first of Shevat is the New Year for the tree;in accordance with the statement of Beit Shammai. But Beit Hillel say: The New Year for trees is on the fifteenth of Shevat.