In Craig Koester's excellent Hebrews commentary, a section is devoted to "The Scriptures." Koester explains how the book of Hebrews uses the Old Testament in its Greek form, and how "Hebrews interprets Christ in light of the OT and the OT in light of Christ" (p. 117). Koester uses a wonderful metaphor to describe this:
Hebrews understands the OT to contain a shadow of what has been revealed in Christ .... The exalted Christ is like a person who stands in the brightness of the sun and casts a shadow upon the earth, so that those who look at the shadow can discern in it the contours of the one who made it. In a similar way, the shadows of the exalted Christ fall on the pages of the OT, allowing the reader to discern in them something of the shape of Christ himself.
Let me urge you to read Hebrews in this manner. A good example comes from this past weekend's Houston Marathon. While I was watching it, I notice that sometimes the street-level cameras would break away for a helicopter view in which the runners' shadows looked like the runners themselves.
Similarly, in Heb. 7:1-10, the author of Hebrews interprets the Old Testament story of Melchizedek (the shadow) in the light of Christ as "a priest forever according to the type of Melchizedek." In the same way, Hab. 2:4 -- "the righteous one will live by faith" -- becomes in Heb. 10:38 a reference to the New Testament people of God who trust Christ for their salvation.
Here's the point. Churches and congregations that are faithful to Christ read the New Testament in light of the Old and vice versa. They would never think of unhinging the Old from the New. The Bible is one book in two volumes, and there can be no Bible without both parts.
Why do I say this with such conviction? Because, as a New Testament student, I am more convinced than ever that to study the New Testament we must study the Old. That's why, when I introduced a course in the Septuagint (the Greek Old Testament) at the seminary, I asked that it be co-taught by one professor from the Hebrew department and one from the Greek. Moreover, students were required to know both Greek and Hebrew before they could enroll for the class. This was almost unheard of back then. But our students needed to see that Christ is to be found in the entire Bible, not just in the New Testament.
We never outgrow our need for truth. Hold fast to the word of God -- the entire word of God. Don't see the truth as out of date because it goes back several millennia. Truth then is truth now. Biblical information is timeless information.