The metaphor is perhaps one of man's most fruitful potentialities. Its efficacy verges on magic, and it seems a tool for creation which God forgot inside one of His creatures when He made him.
— Jos

Under the name of truth I also included beauty, virtue, and every kind of goodness, so that for me it was a question of a conception of the relationship between grace and desire. The conviction that had come to me was that when one hungers for bread one does not receive stones. But at that time I had not read the Gospel.Just as I was certain that desire has in itself an efficacy in the realm of spiritual goodness whatever its form, I thought it was also possible that it might not be effective in any other realm.
— Simone Weil

For books are not absolutely dead things, but do contain a potency of life in them to be as active as that soul was whose progeny they are; nay, they do preserve as in a vial the purest efficacy and extraction of that living intellect that bred them. I know they are as lively, and as vigorously productive, as those fabulous dragon's teeth; and being sown up and down, may chance to spring up armed men.
— John Milton

Books are not absolutely dead things, but do contain a certain potency of life in them, to be as active as the soul whose progeny they are; they preserve, as in a vial, the purest efficacy and extraction of the living intellect that bred them.
— John Milton

I would like to cite an instance which proves the efficacy of clean living on the part of an athlete coupled with the inspiration received from a champion which go a long way to making a champion.
— Major Taylor