“Diligence: Care, promptness, agility and efficiency with which a job is carried out”. Naftali has this particular character trait. He works for the nation, and does his job efficiently. He doesn’t have any personal strength, besides the desire to materialize the ideas of others and the desire to be working for the nation. Therefore, he is regarded as “abounded with [-Hashem’s] favor, and full of Hashem’s blessing”