The First Commandment; In The Bible to the 12 Tribes of the Hebrews - the 12 tribes and Son's of Jacob when

the Hebrews in Goshen where departing Egypt 

Is Exodus 12:1-2;   And God spoke to Moses and to Aaron in the land of Egypt, saying, 2  This New moon is the beginning of  New moons  for you, it is the first New moon of the year. 

https://www.bible.com/bible/316/EXO.12.TS2009 - Look it up on the internet.

1 And Ya'- Ho'- V V- a' spoke to Mosheh [Moses] and to Aharon [Aaron] in the land of Mitsrayim [Egypt] , saying, 2 This New Moon is the beginning of New Moons for you, it is the first New Moon of the year for you. Always starts on the March 21st spring equinox of any year. 

 

This is a Summary Version of Exodus 12, and Stops Here: There are more verses about the "the Passover details" but the point is Exodus 12 is a "Memorial" for the Slain Lamb Jesus, and the remembrance of God's mighty hand delivering the Son's of Jacob from the hand of Pharaoh, the very first "Covenant and Commandment" in the Bible.