A man is said to be insincere who makes a show of willing what he wills not.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/19950/pg19950-images.html

Context

“When God changes man's will from evil to good, man does not approach with insincerity. But God does not always do this. Nor is this the purpose of the sacrament, that an insincere man be made sincere; but that he who comes in sincerity, be justified. Reply Obj. 3: A man is said to be insincere who makes a show of willing what he wills not. Now whoever approaches Baptism, by that very fact makes a show of having right faith in Christ, of veneration for this sacrament, and of wishing to conform to the Church, and to renounce sin. Consequently, to whatever sin a man wishes to cleave, if he approach Baptism, he approaches insincerely, which is the same as to approach without devotion.” source