The operand of THE is a subquery that returns a single column value for you to manipulate. The column value must be a nested table. Otherwise, you get a runtime error. Because the value is a nested table, not a scalar value, Oracle must be informed, which is what operator THE does.
Example
DECLARE
adjustment INTEGER DEFAULT 1;
...
BEGIN
...
UPDATE
THE(SELECT courses FROM department
WHERE name = 'Psychology')
SET credits = credits + adjustment
WHERE course_no IN (2200, 3540);
From Oracle Documentation.