The Hebrew lunar-solar calendar is the true calendar for all mankind. YEHOVAH God Himself established it, and gave it to the children of Israel when they came out of Egypt (Exodus 12:1). At the time of the Exodus, a series of catastrophes occurred that changed the axis and the orbit of the earth and the orbit of the moon, and the ancient year settled into a year of 360 days that lasted until the 8th century B.C. However, the principles of the calendar go back to creation, when the sun and moon were appointed by YEHOVAH "for signs, and for seasons, and for days, and years" (Genesis 1:14. The word for seasons here is moadim, and literally means "an appointment, a fixed time or season; a FESTIVAL, by implication, an assembly" (see Strong's Exhaustive Concordance, #4150). Thus YEHOVAH God appointed the heavenly bodies to determine the "appointed times" of His weekly Sabbaths, annual Holy Days and Festivals from the moment of Creation!
 

The annual Holy Days were intended for all mankind, even as the weekly Sabbath was ordained for all mankind! (Compare Genesis 2:1-3; Mark 2:27-28). Also note that the "Sabbath" -- which includes the annual Sabbaths (Leviticus 23:32, 38-39) -- was "made for MAN" (Mark 2:27) -- not just for the Israelite people! In the coming Kingdom of YEHOVAH God, ALL NATIONS will observe YEHOVAH's annual and weekly Sabbaths according to the lunar-solar calendar (Isaiah 66:23), and go up to Jerusalem for the Feast of Tabernacles (Zechariah 14:16-19) and worship before the Shekinah Glory of YEHOVAH God Himself. Unfortunately, in the 4th Century A.D., the rabbis of Babylonia polluted YEHOVAH's sacred calendar by introducing the continuous week and postponements to prevent certain days from clashing with the Saturday Sabbath which they had created.