How can one fully understand the New without understanding the Old? For example, how can one fully understand The Revelation of St. John without also understanding Jeremiah, Ezekiel, and especially Daniel? Answer: One can not do this. In fact, these three Old Testament books are the precursor to Revelation.
As for me, I take all 66 books of the Bible; the 37 Old Testament books and the 29 New Testament ones. The Valley of the Dry Bones is right before our very eyes.
Dan