“They should confess the sin that they did” (5:7)
The words “that they did” are superfluous.
The Torah is saying that it is not enough to confess the sin. Sin does not occur in a vacuum. Sin occurs in a lifestyle that made the sin possible.
A recovering alcoholic on his 35th anniversary of sobriety said, “The man I once was, drank, and the man I once was will drink again. If I go back to the lifestyle I led before I began drinking, I will drink again.”
When a person confesses a sin, one must also consider “that they did,” i.e., what kind of things did they do that made the sin possible. True teshuva consists of a character change that renders repeating the sin impossible.