A will is the legal instrument that permits a person, the testator, to make decisions on how his estate will be managed and distributed after his death. Years ago there was distinction between a will and a testament, but over time the distinction has disappeared so that a will, sometimes called a "last will and testament." A will serves a variety of important purposes. It enables a person to select his heirs rather than allowing the state laws of descent and distribution to choose the heirs, who, although blood relatives, might be people the testator dislikes or with whom he is unacquainted. A will allows a person to decide which individual could best serve as the executor of his estate, distributing the property fairly to the beneficiaries while protecting their interests, rather than allowing a court to appoint a stranger to serve as administrator. A will safeguards a person's right to select an individual to serve as guardian to raise his young children in the event of his death.
So, the testator bequeaths his property or estate to heirs. To the heirs, what is bequeathed to them is an inheritance. The heirs typically receive the inheritance without having to work for it, it is a gift.
Now, the word "covenant" today means contract, but in the Bible it can be used in two ways. In the Greek, we have two separate words that can be translated by the word "covenant" in English. The words are will and contract. As seen above, a will is made by one person but may affect many. The word translated as covenant in relation to what God gave to Abraham is will. A contract is made between two persons. The giving of the law was like a contract. God gave the law and the Jews said, "All that you have said we will do" (Exodus 24:3).
What we see on Genesis is that the Lord promises an inheritance to certain individuals. The Lord did this with Noah, his sons and all the creatures alive after the flood (Genesis 9:9-11). Neither Noah, his sons, nor the creatures answer back to God, they just received it. The promise of an inheritance was then given to Abraham in Genesis 12,
Ge12:1 Now the LORD had said unto Abram, Get thee out of thy country, and from thy indred, and from thy father's house, unto a land that I will shew thee:
Ge12:2 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:
Ge12:3 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.
Abraham did as God said. This implies that Abraham heard God, and believed Him. The Lord appeared to Abraham in chapter 15 and reiterates the promise. Abraham asked the Lord about who should who should be his heir. The Lord answers I will give you a son "that shall come forth out of thine own bowels" (Genesis 15:4). Then the Lord told Abraham to look at the sky and count the stars. Abraham realized he could not, to which the Lord said, "Your seed will be as numerous as the stars in the sky" (Genesis 15:5). Then verse 6 gives us one of the most important thoughts in the Bible: Abraham, "… believed in the LORD; and he counted it to him for righteousness."
Abraham asked for surety. The Lord had Abraham prepare a sacrifice in the form that business deals were confirmed in his time. Abraham killed the creatures and laid them on the ground according the custom. The custom was for both parties involved in the deal to walk through the sacrifice. But, in verse 17, we find out only the Lord walked through the sacrifice. This showed that God did not make a deal with Abraham. The Lord promised Abraham the inheritance and the Lord would deliver it. Abraham (and his Seed) just received the inheritance by faith.
To the Jews this posed a problem. Why give the Law? What was the purpose? (Wherefore the Law?) Paul answered, that it was added (spoken) "because of transgression" (Galatians 3:19). The law was added because of unbelief. Why did Moses permit divorce? Moses permitted divorce, because of the hardness of their hearts (Matthew 19:7-8). The law was spoken to show the children of Israel, and the world, how sinful they were and how incapable they were of keeping the law. It was spoken to make sin exceedingly sinful (Romans 7:13). It was spoken to make justification by faith desirable. It was never meant to be used as an instrument to achieve righteousness or to be a method for salvation. The law is not an alternate. Nor has the Law disannulled justification by faith.
In Paul's time a Will or Testament could not be changed (by taking away or adding anything) or disannulled after it was confirmed (Galatians 3:15). Paul is saying that the promises made to Abraham and his Seed cannot be modified or disannulled, either (Galatians 3:17). So, the giving of the Law did not change the covenant, nor "make the promise of none effect" (Galatians 3:17). Paul adds on verse 18, "For if the inheritance be of the law, it is no more of promise: but God gave it to Abraham by promise." And, Abraham believed the promise. For this reason, the law was not spoken to Abraham because he believed the promises of the inheritance. Had the children of Israel believe as Abraham believed, there would have been no need to speak the law and write it on tablets of stone. The law would have been written in their hearts