Rashi describes Sara's years as "equal" because she never fully left behind any stage of her life. As she progressed from one phase to the next, she retained the unique characteristics of the earlier stage and refined it as she continued growing.
The opening verse of Parashat Chayei-Sara tells that Sara lived for one hundred and twenty-seven years. The verse then adds a seemingly superfluous phrase: "shenei chayei Sara" – "these are the years of Sara's life." Rashi somewhat ambiguously comments, "Kulan shavin le-tova" – the years of Sara's life were all equal in goodness. According to Rashi, the clause "shenei chayei Sara" emphasizes that the totality of Sara's life was good.
What exactly does it mean that all of Sara's years were "equal," and why is this point worthy of emphasis?
One explanation is cited in the name of the work, "Nachalat Chamisha." Sara lived most of her life with the anguish of infertility, and it was only in the final thirty-seven years that she enjoyed the pleasures of parenthood. One might have therefore considered only those final thirty-seven years the happy, content period of Sara's life, whereas the first ninety were marked by frustration and shame. In truth, however, "kulan shavin le-tova" – all of Sara's years were years of happiness and joy. The Torah here emphasizes Sara's positive attitude throughout her ordeal of infertility, that she never allowed her inability to conceive to interfere with her vitality and enthusiasm towards life.
Rav Soloveitchik zt"l suggested a different explanation of this passage in Rashi (cited in Abraham Besdin's "Reflections of the Rav," vol. 2, chapter 9). He explains that these comments of Rashi must be seen as a continuation of Rashi's previous comments on this verse. In recording Sara's age when she died, the verse writes that she lived "one hundred years, twenty years, and seven years." Rashi notes the obvious difficulty in this formulation, that rather than stating simply that Sara lived "one hundred and twenty-seven years," the verse instead describes three distinct periods – one hundred years, twenty years, and seven years. Based on the Midrash, Rashi explains that the verse seeks to compare these three periods in Sara's life. She was as sinless at one hundred as she was at twenty, and she was a beautiful at twenty as she was at seven. It is with this in mind that we must read the next passage in Rashi's commentary, that "they were all equal in goodness." Rav Soloveitchik explains that Sara managed throughout her life to retain the unique qualities of each stage. Rashi describes here three phases of life: childhood, youth, and adulthood. Rav Soloveitchik explains:
"The child is endowed with a capacity of an all-absorbing faith and trustfulness; youth bursts with zealousness, idealism and optimism; the adult, mellowed with years, has the benefit of accumulated knowledge and dispassionate judgment. Each age is physically and psychologically attuned to particular emphases, but the superior individual can retain and harmonize the positive strengths of all three periods during his entire lifetime."
Rashi describes Sara's years as "equal" because she never fully left behind any stage of her life. As she progressed from one phase to the next, she retained the unique characteristics of the earlier stage and refined it as she continued growing. Even in adulthood, Sara retained the "faith and trustfulness" of her childhood years, as well as the "zealousness, idealism and optimism" of her youth.