If I’m trying to understand something in the Old Testament, then reading widely—or reading across the Testaments—means I’m allowing more authoritative and inspired texts to illuminate the passage I’m studying. Reading widely increases clarity, enriches meaning, and demonstrates the coherence of the Word of God.
The practice of biblical theology is concerned not just with the trees but with the forest—the Big Picture. Biblical-theological instincts want to read parts in light of the whole, and that means seeing specific texts within the larger context of Scripture’s progressive revelation.
Let’s take an example from Genesis 3. According to Genesis 3:1, a serpent came to Eve and began to tempt her to eat from the forbidden tree. Now this serpent isn’t named in the chapter at all. Genesis 3 has twenty-four verses, and throughout them the figure is only called the “serpent.” But who is this oppositional figure? The chapter doesn’t give more information. In fact, the serpent isn’t mentioned throughout the rest of Genesis. Moreover, the serpent isn’t mentioned in the rest of the Pentateuch (Genesis through Deuteronomy).
Yet the interpretive instinct of Bible readers is to understand the tempter in Genesis 3 as Satan. Is that because the serpent is named thus in the chapter? No. The reason Bible readers make that identification is because of later biblical revelation.
In the book of Job, for instance, the being known as Satan wants to destroy Job’s integrity and turn him against the Lord. That agenda sounds like the same goal the serpent of Genesis 3 had for Adam and Eve. In the Gospel of Matthew, Satan comes to Jesus in the wilderness to tempt him by twisting God’s words—a strategy familiar to us because of Genesis 3.