Adam Clarke on Numbers 29:1

And in the seventh month, etc. - This was the beginning of their civil year, and was a time of great festivity, and was ushered in by the blowing of trumpets. It answers to a part of our September. In imitation of the Jews different nations began their new year with sacrifices and festivity. The ancient Egyptians did so; and the Persians still celebrate their nawi rooz, or new year's day, which they hold on the vernal equinox. The first day of the year is generally a time of festivity in all civilized nations. On this day the Israelites offered one young bullock, one ram, seven lambs, and a kid, for a sin-offering, besides minchahs or meat-offerings.