The Most High commanded his people (the Israelites)  remember and reverence his Sabbaths Exodus 31:13 Speak thou also unto the children of Israel, saying, verily my Sabbaths ye shall keep: for it is a sign between me and you throughout your generations; that ye may know that I am the LORD that doth sanctify you.

THE NEW MOON SABBATH

More specifically the beginning of every month the Most High established as the New Moon Sabbath

Psalms 81:3-4 Blow up the trumpet in the new moon, in the time appointed, on our solemn feast day. (4) For this was a statute for Israel, and a law of the God of  Jacob.

2 Chronicles 2:4  Behold, I build an house to the name of the LORD my God, to dedicate it to him, and to burn before him sweet incense, and for the continual shewbread, and for the burnt offerings morning and evening, on the sabbaths, and on the new moons, and on the solemn feasts of the LORD our God. This is an ordinance for ever to Israel. 

It is by the new moons we understand the proper times and seasons to keep the High Holy Days.

Psalms 104:19 He appointed the moon for seasons: the sun knoweth his going down.    

Ecclesiasticus 43:7 From the moon is the sign of feasts, a light that decreaseth in her perfection. 

The New Moon Sabbath was established by the perfection of the Most High’s word and is meant to be observed forever    

Isaiah 66:23  And it shall come to pass, that from one new moon to another, and from one sabbath to another, shall all flesh come to worship before me, saith the LORD. 

THE MEMORIAL OF BLOWING OF TRUMPETS SABBATH

On the first day of the seventh month according to the new moons the Most High commanded us to keep the Sabbath of the Memorial of Blowing of Trumpets.

Leviticus 23:23-24 And the LORD spake unto Moses, saying, Speak unto the children of Israel, saying, in the seventh month, in the first day of the month, shall ye have a Sabbath,    memorial of blowing of trumpets, an holy convocation.

Numbers 29:1 And in the seventh month, on the first day of the month, ye shall have an holy convocation; ye shall do no servile work: it is a day of blowing the trumpets unto you.

These High Days as well as the other High Holy days were created by the wisdom of the Most High and it is commanded that we keep these days as it is written.

Ecclesiasticus 33:7-9   Why doth one day excel another, when as all the light of every day in the year is of the sun? By the knowledge of the Lord they were distinguished: and he altered seasons and feasts. Some of them hath he made high days, and hallowed them, and some of them hath he made ordinary days.