The New Covenant
Three events occurred as God revealed His plans for man. First a promise was made to Abraham.
Gen 12:1-3 Now the LORD had said unto Abram, Get thee out of thy country, and from thy kindred, and from thy father's house, unto a land that I will shew thee: (2) And I will make of thee a great nation, and I will bless thee, and make thy name great; and thou shalt be a blessing: (3) And I will bless them that bless thee, and curse him that curseth thee: and in thee shall all families of the earth be blessed.
Both future events hinged from this promise. The future events did not change the promise, but fulfilled it.
Gal 3:14-18 That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith. (15) Brethren, I speak after the manner of men; Though it be but a man's covenant, yet if it be confirmed, no man disannulleth, or addeth thereto. (16) Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ. (17) And this I say, that the covenant, that was confirmed before of God in Christ, the law, which was four hundred and thirty years after, cannot disannul, that it should make the promise of none effect. (18) For if the inheritance be of the law, it is no more of promise: but God gave it to Abraham by promise.
This verse shows the enduring promise and mentions the second event, which was the giving of the Law of Moses.
Gal 3:19 Wherefore then serveth the law? It was added because of transgressions, till the seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator.
We see the Law of Moses, often just called the law, was a “means to the end of the promise”. It was not to replace the promise, but to aid in fulfilling the promise. The law was given to show men what sin was and help man realize his sinful state. The condemnation of the law also helped mankind realize the need for a Savior.
The third and final event was Christ establishing His new covenant.
Gal 3:13 Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree:
Gal 3:24-25 Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith. (25) But after that faith is come, we are no longer under a schoolmaster.
All authority was given to Christ in heaven and in earth (Matt 28:18) and we need to heed the gospel of Christ if we desire to be saved.
Act 4:12 Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved.