Why were the Corinthians unable to understand the truths of Ephesians?
The Corinthians were carnal rather than spiritual, having been saved out of abject paganism and its immorality. They had not come far enough to understand the position in the heavenlies, and even Paul had not yet raised those Ephesians truths.
Les teaches that the Corinthians were carnal, not a spiritual congregation, and were nowhere near understanding Ephesians because they hadn't come that far yet. They had been saved out of abject paganism and all its attendant immorality, but understanding their position in the heavenlies was beyond them at that point. Even the Apostle Paul had not yet mooted that truth. So he begins with what he can write to them, such as I Corinthians 1:6-7.