In this direction finality is not sought, for it is apparently unattainable. All that we can say is, in the words of a leading analyst, "sufficient unto the day is the rigor thereof."
Notas sobre a tradução
E.T.Bell wrote that. I read this cite as is, without surrounding context from the same author. I'm most interested in the part between quotes, because I think I understand the rest.
Seems that what E.T.Bell meant is that a proof, in mathematics, is good enough if it rigorously correct in the patterns of today, even if these patterns will change in the future (as it has changed through history). I think that the author of the phrase that you wrote here is just saying that he do what is possible not what would be ideal.