The thing I find most irrational about dispensationalists is that while they claim to take OT prophecies literally and criticize those who spiritualize OT prophecies-- clearly Jesus and the Apostles spiritualized OT prophecies and they accept those interpretations as legitimate but cast aspersions on Christians who follow Jesus and the Apostles method of interpretation.
Many Christians have been duped into the belief that anything Jewish automatically translate into faithfulness. After all, the reasoning goes, the Bible was written primarily by Jewish people so who better to understand what’s there than other Jews? They fail to grasp the harsh reality that much of the writings and practices of the Jews comes after the time of Christ, and were written consciously as an apologetic against Christ and Christianity. Is it surprising, then, to find Jewish teachers who would reinterpret the OT prophets in such a way as to deny how the NT writers understood those prophets wrt Jesus Christ, His person and work?
They also fail to discern the fact that these post-resurrection Jewish authors were not divinely inspired. In fact, some folks might go so far as to suggest that they were satanically inspired, since one must either be in the kingdom of light or the kingdom of darkness. There is no middle ground. E.g., Is a Jewish writer who denies Christ a better source of truth than a Muslim writer who denies Christ?
The Bible is all about Jesus Christ. The Law and the Prophets testify of Him. The divinely-inspired NT writers were able to connect the dots. What some “Christian” theologies have attempted to do is run a dividing wedge through the Bible and say that some texts are not really about Christ and the Christian faith, but about Israel, the earthly people of God. They do this by adopting a so-called “literal” interpretation of the Bible, but, in fact, all they are doing is dismissing the NT approach to interpreting the Old, and adopting the same approach that unbelieving Jews have utilized to say that this or that passage is not about Jesus.