despising useless knowledge

[St. Basil the Great] contented himself with learning the
general principles of geometry, medicine, and the like sciences,
rightly judging such an insight into all the arts of extreme use
to a person who would excel in any of them, but despising whatever
seemed useless to one who had devoted himself solely to
religion and piety. In checking thus his curiosity and natural
thirst after knowledge, according to the excellent reflection of
St. Gregory Nazianzen, he was not less admirable for what he
neglected in the sciences than for what he had learned. Source