Yahweh's promises and instructions to His people of Israel concerning what He expected from Israel were clearly given in the Old Testament. The New Testament makes these verses more binding because the Holy (set-apart) Spirit was sent on Pentecost to remain on earth. We now seek the deeper spiritual sense and applications of His word and obey from the heart. Yahweh teaches spiritual truth and understanding from physical lessons. This is especially true of Pentecost and the Feast days.
Yahweh's initial Covenant (agreement) took place with Israel after they left Egypt and came to Mount Sinai. The ratifying of the Covenant by Israel took place on Pentecost or 'Feast of Weeks:'
And all the people answered together, and said, All that Yahweh hath spoken we will do. And Moses returned the words of the people unto Yahweh. (Ex 19:8 AV)
[Chapter 20 lays out the Ten Commandments]
And Moses came and told the people all the words of Yahweh, and all the judgments: and all the people answered with one voice, and said, All the words which Yahweh hath said will we do. (Ex 24:3 AV)
Three requirements for Yahweh's appearance were the cleansing of the body and clothing (Ex 19:10), confining Israel to the camp and limited freedom with sexual abstention (Ex 19:15). [Example see 1Sam 21:4-5] This precaution shows the seriousness and holiness of allowing the Spirit of Yahweh to remain on earth in Acts chapter two.
The New Testament was built on the Old Testament often with direct quotes for proof that these indeed are Yahweh's Words. Having been given the Holy Spirit through our baptism, we find the New Testament opens our spiritual understanding to a higher level, allowing us to have Yahweh's point of view and see things from His vantage point. If every human kept the Commandments, what a great world this would be! We are in training now to live our lives in obedience to Yahweh's laws.
Pentecost brought with it a big difference in the New Testament. In the Old Testament the Holy (Set apart) Spirit was given when needed, but was taken back to Yahweh when it had accomplished the task. Now, Yahweh's Spirit became available to Yahweh's baptized people and remains on earth (Acts 1:4-5). Since Calvary the Holy Spirit is indwelling Yahweh's obedient people and helps us keep the Law:
This [is] the covenant that I will make with them after those days, saith Yahweh, I will put my laws into their hearts, and in their minds will I write them. (Heb 10:16 AV) See also Heb 8:8-10.
The Old Testament teaches that a year old male lamb and a grain and drink offering were a part of the Pentecost service and the burnt offering and two loaves according to Leviticus 23:9-21 were a special offering on Pentecost:
And he sent young men of the children of Israel, which offered burnt offerings, and sacrificed peace offerings of oxen unto Yahweh. (Ex 24:5 AV; etc.)
The New Testament says we can have Yahweh's attention at anytime and address Yahweh if we sincerely seek Him and no animal sacrifice is required for we now have faith in Yahshua now to put into practice what we have learned:
By a new and living way, which he hath consecrated for us, through the veil, that is to say, his flesh. (Heb 10:20 AV)
But the hour cometh, and now is, when the true worshippers shall worship the Father in spirit and in truth: for the Father seeketh such to worship him. Elohim [is] Spirit: and they that worship him must worship [Him] in spirit and in truth. (Joh 4:23-24 AV)