http://insearchoftruth.org/articles/testaments2.html
The Old and New Testaments
Introduction
"New Testament? Old Testament? What is the difference, and why does it matter?" Understanding the difference between the Old and New Testaments is one of the most important foundations that must be laid to properly understand God's Word. Failing to realize the Bible's teaching on this matter can lead to countless erroneous conclusions, possibly costing one's own soul. Therefore, let us turn to the pages of God's Word for an in depth study to let it tell us the difference and significance of the Old and New Testaments. You may rather prefer to first read a summary of the conclusions formed here in detail, with Scriptures.
"What's a Testament"?
The word "testament" can have different meanings depending on the context, so the first thing to do is to define the word "testament" as the Bible uses it. Some religious organizations wish to use one meaning of the word that makes it the testimony of a witness. Therefore, the Old and New Testaments would respectively be older and newer testimonies about God and His people. Adopting this meaning conveniently opens the door for them to usher in an even newer testament, another revelation from God. However, the Bible teaches that it is already final, complete, and nothing will ever be added to it. So how does the Bible use the word?
"For where there is a testament, there must also of necessity be the death of the testator. For a testament is in force after men are dead, since it has no power at all while the testator lives." Hebrews 9:16-17
From this verse we see that the Bible uses the another meaning of the word "testament". It is used in the sense of "last will and testament", or as what we commonly call just a "will". So, the testaments are a type of will, an issue of instructions to be carried out once the one giving the will has died. Therefore, the New Testament is Christ's last will and testament for us to keep now that he has left the earth. However, the word "testament" is one of multiple descriptive words used by the Bible. Before we go further, let us examine the above verse in its broader context and pick up another description along the way.
"But Christ came as High Priest of the good things to come, ... Not with the blood of goats and calves, but with His own blood ... For if the blood of bulls and goats and the ashes of a heifer, sprinkling the unclean, sanctifies for the purifying of the flesh, how much more shall the blood of Christ, who through the eternal Spirit offered Himself without spot to God, cleanse your conscience from dead works to serve the living God? And for this reason he is the mediator of the New Covenant by means of death, for the redemption of the transgressions under the first covenant, that those who are called may receive the promise of the eternal inheritance. For where there is a testament, there must also of necessity be the death of the testator. For a testament is in force after men are dead, since it has no power at all while the testator lives. Therefore not even the first covenant was dedicated without blood. For when Moses had spoken every precept to all the people according to the law, he took the blood of calves and goats, with water, scarlet wool, and hyssop, and sprinkled both the book itself and all the people, saying 'This is the blood of the covenant which God has commanded you.'" Hebrews 9:11-20
So why was the word "testament" chosen? It served as an illustration to explain the bounds of the covenants and one of the reasons that necessitated Christ's death. For some reason not explained here, it is necessary for blood to be shed for us to receive forgiveness of sins.
And according to the law almost all things are purified with blood, and without shedding of blood there is no remission. Hebrews 9:22
But the word more often used in the Scriptures, and the word we see in the above context, is the word "covenant". This word describes another facet of these testaments. They are not just a last will and testament, but rather a divine agreement extended by God. The New Testament, or Covenant, is a promise from God that He will save us if we obey His Testament. How does God do this? By the blood of Jesus Christ. In fact, Christ Himself used this terminology in the instituting of the Lord's supper:
For this is My blood of the new covenant, which is shed for many for the remission of sins. But I say to you, I will not drink of this fruit of the vine from now on until that day when I drink it new with you in My Father's kingdom."Matthew 26:28-29
Therefore, the Old and New Testaments are writings that contain the "last will and testament" of God that enables us to enter a covenant relation with Him. One of the central blessings of this covenant relationship is salvation.
The Distinction: The Imperfect Covenant
"So what's the difference? Why have an Old and New Covenant?" The answer to this can actually be found in the above verses, however the following passage may help to make the point even clearer:
For it is not possible that the blood of bulls and goats could take away sins. ... And every priest stands ministering daily and offering repeatedly the same sacrifices, which can never take away sins. But this Man, after He had offered one sacrifice for sins forever, sat down at the right hand of God, from that time waiting till His enemies are made His footstool. For by one offering He has perfected forever those who are being sanctified." Hebrews 10:4, 11-14
Both covenants were ushered in by "the shedding of blood" - blood of animal sacrifices for the Old, and the blood of Christ for the New. Rereading these passages from Hebrews, we learn that Christ's blood of the New Covenant does what could not be done in the Old - forgive sins. So, did Old Testament saints not receive forgiveness of sins? If we reread Hebrews 9:15, we will learn that Christ's blood also worked retroactively and saved those Old Testament saints who had been faithful in keeping the animal sacrifices, which were symbols of the ultimate sacrifice to come.
Even the Old Testament prophets hundreds of years before, foretold the coming of a second covenant. Listen to the words of the prophet Jeremiah:
Behold, the days are coming' says the Lord, 'when I will make a new covenant with the house of Israel and with the house of Judah - not according to the covenant that I made with their fathers ... which they broke, though I was a husband to them. But this is the covenant that I will make with the house of Israel after those days, says the Lord: I will put My law in their minds, and write it on their hearts; and I will be their God, and they shall be My people. No more shall every man teach his neighbor, and every man his brother saying, "Know the Lord," for they all shall know Me, from the least of them to the greatest of them,' says the Lord. 'For I will forgive their iniquity, and their sin I will remember no more.'" Jeremiah 31:31-34
In addition to confirming God's plan to have two covenants, this passage also does a great deal to explain the components of the covenant. Please read the last part again with this in mind.
The New Testament also teaches that Old Testament was imperfect because it could not offer forgiveness of sins. Instead, it "rolled back" the sins each year, until the offering of Christ's ultimate sacrifice. The entire book of Hebrews is specifically focused on showing that the Old Covenant is inferior to the New, and that New Testament Christians should not abide by this inferior covenant when they have something so superior. In fact, the writer of Hebrews actually quotes the above passage from Jeremiah to make this point (Hebrews 8:6-13).
Another significant difference is who was given the covenants. The Old Testament was a covenant given strictly for the Jews, or Israelites. Non-Jews, or Gentiles, could adopt the Jewish covenant and become "prostelytes", but there was no special law and relationship offered that was for the Gentiles as the Old Testament was for the Jews. However, the New Testament made no distinction. One of the great things about the New Testament is that God's message and special covenant relationship is extended to all races and peoples. Consequently, the writings of the Old Testament generally track the story of the Israelites with a few exceptions, and the New Testament writings contain the gospel of Jesus and of the spread of the gospel all over the world, as well as directions for the new Christians.
The Application
So what is the application for us today? There are two things we should learn: One, the Old and New Testaments are synonyms for Old and New Covenants, not testimonies. Second, the Old Testament was done away at the cross by Christ's death, which ushered in the New Testament. Therefore, we are no longer under obligation to keep the laws of the Old Testament, neither is it authoritative to justify our actions today. But rather, we are bound to the New Testament and to use it for authority. Please read this passage in which Paul uses the analogy of the law of marriage to further describe the nature of the two covenants:
Therefore, my brethren, you also have become dead to the law through the body of Christ, that you may be married to another - to Him who was raised from the dead, that we should bear fruit to God." Romans 7:4
Some may wonder if just the ceremonial law was done away and if the 10 commandments still remain. This question is resolved by looking further down in the context where Paul refers to the law again, "For I would not have known covetousness unless the law had said, 'You shall not covet.'" (Romans 7:7). Therefore, the law that was done away also included the 10 commandments, which was directly referenced in this verse. God confirmed this upon the Mount of Transfiguration when He instructed the apostles to listen to Christ for authority and not to Moses and the prophets (Matthew 17:1-6 and Deuteronomy 18:15-22). Please see also Colossians 2:11-17.
The third and final lesson is that the Old Testament has been done away as an authority for how to be saved and how God's church should operate. However, the Old Testament is not been made worthless, but it serves as a great source of examples that are necessary for our spiritual growth and health (I Corinthians 10:6, 11-12; Romans 15:4).
Conclusion
Therefore, let us always bear this distinction in mind. We must be diligent to use the New Testament as authority, and to use the Old Testament examples in their proper place. If we do this, we will solve many of the disagreements that separate those who would worship God. With this fundamental pillar in place, we are now ready to examine the actual process of establishing Biblical authority, "doing all in the name of the Lord".
To read an exchange and more discussion on this topic, please visit our forums.