It is important to understand that both Covenant Theology and Dispensational Theology attempt to take the bible seriously. Both groups believe in the full inspiration and use the historical grammatical approach. The difference lies in the presuppositional approach to the Bible itself. As Michael Vlach states citing Feinberg
“Nondispensationalists begin with NT teaching as having priority and then go back to the OT. Dispensationalists often begin with the OT, but wherever they begin they demand that the OT be taken on its own terms rather than reinterpreted in the light of the NT.”
These methodologies or approaches to the Bible are the fundamental causes as to why men differ in their understanding of Israel and affect our understanding of the nature of the New Covenant.