Why couldn't the Corinthians understand the teaching of Ephesians?
The Corinthians were carnal and not a spiritual congregation, having been saved out of abject paganism and its immorality. They had not progressed far enough in spiritual understanding to grasp their position in the heavenlies, and even Paul had not yet introduced that teaching.
Les explains that the Corinthians were carnal, not a spiritual congregation, and nowhere near understanding Ephesians. They had been saved out of abject paganism and all its attendant immorality, but they hadn't come that far yet. To understand this position in the heavenlies? No, they hadn't gotten that far. Even the Apostle Paul hadn't mooted that yet. So instead, he writes what he can tell them, beginning in I Corinthians 1:6-7.