This week's parshah begins with the passing of Sarah Imeinu.
In connection to this possuk, the Midrash cites a possuk in Tehillim: יודע ה' ימי תמימם ונחלתם לעולם תהיה - Hashem knows the days of the perfect, and their inheritance will be forever (תהילים לז יח). Simply, this possuk is referring to the days of tzaddikim, saying that Hashem will repay them with eternal reward. However, here Chazal explain it adding another dimension. כשם שהם תמימים כך שנותיהם תמימים - just as they [the tzaddikim] are wholesome, so too, their days in This World are wholesome.
Accordingly, the possuk is not referring to the tzaddikim themselves, but to the way they spend their lives. They are praised for the way in which they spend every day in this world; they completely perfect their days. This, says the Midrash, is what we are praising Sarah for.