Why do Paul's letters stand by themselves in the New Testament?

Les explains that these letters of the Apostle Paul stand in the center of the New Testament pretty much by themselves because this is the part of the Word directed primarily to the Gentile Church, or the Body of Christ. He contrasts this with the Old Testament and the Gospels in the early chapters of Acts, which were all directed to and under the auspices of the nation of Israel. When Israel continued to reject everything and would not believe that Christ was the promised Messiah, God providentially took away their Temple, took away the city of Jerusalem, uprooted the nation from the land, and put them out into the nations in dispersion. He then turned instead to the pagan Gentile world beginning with the Apostle Paul. Les also reminds listeners of what Paul put up with to get the Gospel to Gentiles, including suffering listed in II Corinthians, shipwreck on the island of Malta, and being three times in the deep.