Why did Paul reveal truths about the Holy Spirit that are not in the Gospels?
The truths depended on events that had not yet occurred. The Holy Spirit had not yet come and Christ had not yet died, so those things had to be held in abeyance until they happened. Only then could the Apostle Paul reveal them, making them Pauline and not found in the Gospels.
Les teaches that the Holy Spirit had not yet come and Christ had not yet died, so these truths had to be held in abeyance until those events occurred. Now, afterward, the Apostle could reveal them. This is why Ephesians 1:14 speaks of the earnest or down payment of our inheritance until the redemption of the purchased possession, and why Ephesians 2:1, 4, 8-9 speak of being quickened, God's mercy and love, and salvation by grace through faith. Les says that is Pauline; you won't find that back in the Gospels.