I think it makes sense that God revealed his feasts to his followers very early. For example:
Gen 14:18 Then Melchizedek king of Salem brought out bread and wine; he was the priest of God Most High.
Melchizedek was a priest of God. Apparently there was some sort of worship system in place. I think it's reasonable to assume that Israel got immersed into the pagan culture of Egypt and had to be reacquainted with the ways of the Lord after coming out of captivity.
Yup.....you're right! My favorite example has always been: [Genesis 22:1-8] 1 And it cometh to pass after these things that God hath tried Abraham, and saith unto him, 'Abraham;' and he saith, 'Here am I.' 2 And He saith, 'Take, I pray thee, thy son, thine only one, whom thou hast loved, even Isaac, and go for thyself unto the land of Moriah, and cause him to ascend there for a burnt-offering on one of the mountains of which I speak unto thee.' 3 And Abraham riseth early in the morning, and saddleth his ass, and taketh two of his young men with him, and Isaac his son, and he cleaveth the wood of the burnt-offering, and riseth and goeth unto the place of which God hath spoken to him. 4 On the third day -- Abraham lifteth up his eyes, and seeth the place from afar; 5 and Abraham saith unto his young men, 'Remain by yourselves here with the ass, and I and the youth go yonder and worship, and turn back unto you.' 6 And Abraham taketh the wood of the burnt-offering, and placeth on Isaac his son, and he taketh in his hand the fire, and the knife; and they go on both of them together. 7 And Isaac speaketh unto Abraham his father, and saith, 'My father,' and he saith, 'Here am I, my son.' And he saith, 'Lo, the fire and the wood, and where the lamb for a burnt-offering?' 8 and Abraham saith, 'God doth provide for Himself the lamb for a burnt-offering, my son;' and they go on both of them together.
God has selected Isaac on the 10th day [Exodus 12:3] and in our example [Genesis 22:2].
The next day (verse 3) Abraham gets up, takes Isaac and two of his men and sets out for Mt. Moriah. This would be the 11th day of the month. Mt. Moriah is Jerusalem itself, [II Chronicles 3:1].
On the 3rd day from the morning they set out (verse 4, now the 14th of the month)[Exodus 12:6] they see the place in the distance and Abraham, telling his men to await him..... takes his boy up the mountain. He makes Isaac carry the wood for the sacrifice the same as a later Son, who was sacrificed by His Father also.....carried His own wood in the form of a crucifixion stake. This latter sacrifice also took place on Mt. Moriah..... on Passover in preparation for The Feast of Unleavened Bread. It also was a Lamb of God (verse 8) that was sacrificed [I Peter 1:19].
Verse 2 is the first place in the scriptures where love for another human being is expressed, and it speaks of a father's love for his son. Isaac is called Abraham's "Only" son (verse 2) much the same as this scripture tells us: [John 3:16] For God so loved the world, that he gave his "Only" begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
Also [John 3:35] The Father loveth the Son, and hath given all things into his hand.