Alma ends his plea for Corianton to repent by sending him to his elder brothers for counsel. At the end of both the counsel to Helaman and Shiblon, Alma had said “farewell.” There must have been some foreknowledge that Alma would not be around for much longer. For that reason, he sends Corianton to his faithful brothers.
The counsel has been to repent, and now the admonition is to cease to “be led away by any vain or foolish thing,” including whatever it meant to go after “those wicked harlots.” That was certainly a part of his sin, even if the greater sin was leading to the hardening of hearts. It was his bad example that was the problem. Modern readers also understand how difficult it is to follow leaders who fail to live up to their stated ideals. When that occurs within the Church, it is particularly difficult and may lead to many hardening their hearts. Those who do so are in great sin.