I have discovered teaching over the years that part of the problem that people don’t know how to interpret the NT occurs because they don’t know their OT. Most of the NT derives its definitions, teaching, promises and ideas from OT doctrine.
Without knowing and studying the OT and reading the NT is like walking into the middle of a movie and trying to guess the plot and where is going. Some movies are easier than others to figure out if one walks in at the halfway point, but others that have a complex plot, lots of dialogue, and many twists will be extreme hard to figure out. Hence, the Bible is that movie. Although many would like to think the Bible is very simple, and it does have its simple aspects called the milk of the Word (1 Cor. 3:2; Heb. 5:12-13; 1 Pet. 2:2), it has much more complex elements (e.g., Peter calls Paul’s teaching Scripture and hard to interpret, see 2 Pet. 3:15-16) that to understand involves one leaving home early to catch the beginning of the picture.
In other to get the picture (pun intended) see how much of the OT appears in all NT books. Hence, those who miss studying the OT will, no doubt, be misinformed in understanding the NT. It’s been said: “The New Testament is concealed in the Old, and the Old is revealed in the New.” Or to say it another ways is, “the Old is the New concealed and the New is the Old revealed.”
This superb chart shows this very point and the importance of these statements by highlighting the percentages and verses that one finds of the OT revealed in all NT books.