If a person has a fair amount of exposure to Mainstream Christianity, and a familiarity with the Bible, he may notice that Mainstream Christianity often de-emphasizes the Old Testament and puts a disproportionate amount of emphasis on Paul's epistles. I would hesitate to say that any part of the Scriptures can be overemphasized. However, if we give uncalled-for weight and emphasis to certain parts of the Bible, and neglect what the rest of the Scriptures teaches about an issue, we will probably develop and imbalanced view of that particular issue.
By volume, Paul's epistles make up approximately 5% of the Bible. Paul's writings are holy Scripture, but neither Paul nor the Holy Spirit expected us to give more weight and authority to these epistles than we do to the Old Testament or to the rest of the New Testament.
By putting a disproportionate amount of emphasis on these letters that Paul sent to various churches, we fail to follow the example of Paul, who told the Ephesians, "I have not shunned to declare unto you all the counsel of God" (Ac.20:27). By neglecting certain parts of the Bible, we ignore Paul's declaration that "all Scripture is inspired and is useful." (2 Tim. 3:16).
Discover more in the full article, The Ghost of Marcion.