The Bible is composed of the Old and New Testaments. These are really the Old and New Covenants.
The Old Covenant is the one that God made with the nation of Israel at Sinai.
Exodus 19:3 And Moses went up unto God, and the LORD called unto him out of the mountain, saying, Thus shalt thou say to the house of Jacob, and tell the children of Israel; 4 Ye have seen what I did unto the Egyptians, and how I bare you on eagles’ wings, and brought you unto myself. 5 Now therefore, if ye will obey my voice indeed, and keep my covenant, then ye shall be a peculiar treasure unto me above all people: for all the earth is mine: 6 And ye shall be unto me a kingdom of priests, and an holy nation. These are the words which thou shalt speak unto the children of Israel. 7 And Moses came and called for the elders of the people, and laid before their faces all these words which the LORD commanded him. 8 And all the people answered together, and said, All that the LORD hath spoken we will do. And Moses returned the words of the people unto the LORD.
Exodus 24:7 And he took the book of the covenant, and read in the audience of the people: and they said, All that the LORD hath said will we do, and be obedient. 8 And Moses took the blood, and sprinkled it on the people, and said, Behold the blood of the covenant, which the LORD hath made with you concerning all these words.
Israel failed to keep the Covenant and God promised that he would make a New Covenant.
Jeremiah 31:31 Behold, the days come, saith the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah: 32 Not according to the covenant that I made with their fathers in the day that I took them by the hand to bring them out of the land of Egypt; which my covenant they brake, although I was an husband unto them, saith the LORD: 33 But this shall be the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people. 34 And they shall teach no more every man his neighbour, and every man his brother, saying, Know the LORD: for they shall all know me, from the least of them unto the greatest of them, saith the LORD: for I will forgive their iniquity, and I will remember their sin no more.
This New Covenant is the one inaugurated by Jesus Christ.
We enter this New Covenant when we believe the gospel, repent of our sinful way of life and are baptised into Christ for the remission of our past sins.
Hebrews 8:8 For finding fault with them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant with the house of Israel and with the house of Judah: 9 Not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they continued not in my covenant, and I regarded them not, saith the Lord. 10 For this is the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people: 11 And they shall not teach every man his neighbour, and every man his brother, saying, Know the Lord: for all shall know me, from the least to the greatest. 12 For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more. 13 In that he saith, A new covenant, he hath made the first old. Now that which decayeth and waxeth old is ready to vanish away.
Hebrews 9:15 NKJV For this reason he (Jesus Christ) is the mediator of a new covenant, so that those who are called may receive the promised eternal inheritance, because a death has occurred that redeems them from the transgressions under the first covenant.
Those in Christ are not under the Old Covenant but the New.
This means that we are not under the Law of Moses but under the Law of Christ.
Galatians 6:2 Bear ye one another’s burdens, and so fulfil the law of Christ.
1 Corinthians 9:21 To them that are without law, as without law, (being not without law to God, but under the law to Christ,) that I might gain them that are without law.
The Law of Christ consists of his commandments which are found in the New Testament.
Matthew 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit: 20 Teaching them to observe all things whatsoever I have commanded you…
John 14:15 If ye love me, keep my commandments.
I hope you find this helpful.