“Ani HaShem Lo Shaniti” (I am God, I do not change) Malachi 3:6. Not only is God eternal, we don’t add to or detract from Him by our mitzvah observance or lack of it.
Nonetheless, each of us is called to perform all of the mitzvot available to us in any given time or place. However, we’re never told how, beyond merely fulfilling our obligations, any benefits (remember God does not benefit) that accrue.
Further, our abilities in relationship to mitzvot in general, and any specific mitvah changes over time. Our learning skills (including Hebrew language skills–not taken for granted in any generation of the Jewish People) hopefully increase through our lives, but there are times that illness and injury can actually diminish them. Certain mitzvot can only be done in Eretz Yisrael, some only outside of it. Some are almost an accident of birth (are we a Cohain, Levi, Yisrael?) Some are only appropriate during certain age spans (counting in a minyan or participating in Temple Service, others from the moment we’re first able to manage them (reciting the Sh’ma, for example).
In each case, our attitude in approaching each mitzvah is supposed to be fresh, enthusiastic, simple and selfless.
Do we try to improve our performance each opportunity? That certainly seems worthwhile. What happens when a radically lesser perf0rmance is the best we can do?
If you look back at my previous essay, Praying From The Floor, you’ll see that right now that there are occasions I can barely recite the Shema and the Amida at all. Just a very few months ago I had, for any years, added new readings to each of the three daily services (most recently–a new psalm from Tehillim and one of the Ramchal’s deep prayers/meditations before beginning the standard fare in the siddur). Today I feel fortunate indeed if I can read the absolute minimum accepted for each of the tefillot and there are many days when even that is beyond my endurance. And, at the same time, many of my recent prayer experiences have seemed vastly deeper, more intimate and superior to any I’ve experienced in the past.
I doubt if there is a definitive answer or accepted viewpoint for any of these questions. But they are compelling, at least for me, to consider.