Although the use of the word “ply” is a bit archaic, it’s still used a lot in India. I remember seeing the words inscribed on a wall over an elevator. They said, “Lift plying to odd floors only.” Nevertheless, Srila Prabhupada’s use of the word has a kind of poetry, especially when he speaks of the human body, which is compared in the scriptures to a suitable boat, built to ply safely across the often dangerous ocean of material existence.The competent captain of this sailing ship is the spiritual master and favorable winds are likened to the sastras.