"The Old Testament is indispensable in understanding the New... the New Testament is the climax to a story, if you don't know the first part of a story then the ending doesn't mean that much" - Bishop Robert Barron
I've written a few articles on my blog, in a series called The Story of Salvation (Link here), and I just thought I'd take a break from the story to say why it's even important to know and understand the Old Testament.
Why read the Old Testament?
The two sections of scripture are divided into, what we now call, the Old Testament and the New Testament. The dividing line between the two being, just like in history with BC and AD, the birth of the Son of God.
The New Testament contains the words, teachings, and commands of Christ, in both His own words and those of the inspired authors. The Old Testament contains the history of the people of God, the law, and the prophets.
You might ask why learning about Israel, the law of Moses, and the prophets, should be of any concern to a Christian. There are many reasons, but the main one that I would proffer is this; Christianity is the fulfillment of thousands of years of prophesy about a Jewish messiah, with Jewish apostles and disciples, who were steeped in Jewish religion and tradition.
It's this base that Christianity is built upon. It's for this reason that the Old Testament is important, so important that the first reading at Mass will almost always be from the Old Testament (except during Easter season, when the first reading is from the book of Acts).
Also it's through the Old Testament that we can get the context of scripture as a whole.
What good is it to say, during the creed, that Jesus "rose again on the third day in accordance with the Scriptures," if we don't know what scriptures it's referring to? It's the unity of the whole body of scriptures that gives everything it's meaning. As the Catechism says;
CCC 140: The unity of the two Testaments proceeds from the unity of God's plan and his Revelation. The Old Testament prepares for the New and the New Testament fulfills the Old; the two shed light on each other; both are true Word of God
(See also 1 Corinthians 10:11 & Romans 15:4)
Jesus taught, using the Old Testament
When Jesus taught His disciples, and the crowds that gathered, He taught in parables and by making references to the scriptures. That means He was making direct references to the Hebrew Scriptures, aka the Old Testament, because there was no New Testament at the time.
Even after Christ's death and resurrection, there wasn't any written scriptures, except the Old Testament, until the first gospel was written in about 65AD. So when the inspired writers of the New Testament made reference to "the scriptures" it was always the Old Testament because the new hadn't yet been written.
For example, the phrase "the scriptures" is said 20 times in the Gospels, 7 times in Acts, 6 times in Romans, 3 times each in Galations and James, 2 times each in 1 Timothy and 1 Corinthians, and once in 2 Peter. Each and every time, this is a reference to the Old Testament. And that's just with a concordance word search, there are more than these if you searched different terms, but the point is the same.
Just because it's interesting
There are a whole host of theological, ecclesiological, soteriological, and eschatological reasons to read and study the Old Testament, but let me present and equally valid one; it makes for a good read!
There are countless stories in the Hebrew Scriptures, and some are more interesting than the bestselling novels of today. Adam and Eve, Noah and the flood, Abraham and Sarah, Abraham and Isaac, Jacob and his brother, Joseph and his brothers, Moses the prince and savior of the Hebrews, the Red Sea, golden calf, and these are all just in Genesis!
Get out there and read the Old Testament, study the way that the ancient Israelites worshipped God, and study the prophecies that pointed clearly to Jesus as the messiah. I promise you it will strengthen your faith, and add to it a level of depth that you didn't even know you were missing.
Some final words from the Catechism
The catechism has a lot to say about the eternal value of the Old Testament, and why Christians, of all stripes, should read and study it. Here's just a few more paragraphs from the catechism to show how much the Church values the whole body of scripture
CCC 121: The Old Testament is an indispensable part of Sacred Scripture. Its books are divinely inspired and retain a permanent value,for the Old Covenant has never been revoked.
CCC 122: Indeed, "the economy of the Old Testament was deliberately so oriented that it should prepare for and declare in prophecy the coming of Christ, redeemer of all men." "Even though they contain matters imperfect and provisional," the books of the Old Testament bear witness to the whole divine pedagogy of God's saving love: these writings "are a storehouse of sublime teaching on God and of sound wisdom on human life, as well as a wonderful treasury of prayers; in them, too, the mystery of our salvation is present in a hidden way."
CCC 123: Christians venerate the Old Testament as true Word of God. The Church has always vigorously opposed the idea of rejecting the Old Testament under the pretext that the New has rendered it void (Marcionism).