Internet-delivered interventions are generally effective for psychological problems. While the presence of a clinician guiding the client via text messages typically leads to better outcomes, the characteristics of what constitutes high-quality communication are less well investigated. This study aimed to identify how an internet therapist most effectively communicates with clients in internet-delivered cognitive behavioral therapy (ICBT). Using data from a treatment study of depressed adolescents with a focus on participants who had a positive outcome, messages from therapists were analyzed using thematic analysis. The study focused on the therapist's 1) encouragement and 2) affirmation, and how the therapists used 3) personal address. The analysis resulted in a total of twelve themes (Persistence Wins, You Are a Superhero, You Make Your Luck, You Understand, Hard Times, You Are Like Others, My View on the Matter, Time for a Change, Welcome In, Let Me Help You, You Affect Me, and I Am Human). Overall, the themes form patterns where treatment is described as hard work that requires a motivated client who is encouraged by the therapist. The findings are discussed based on the cognitive behavioral theoretical foundation of the treatment, prior research on therapist behaviors, and the fact that the treatment is provided over the internet.