His contemporaries bear testimony to the energy and perseverance with which he laboured towards self-perfection from his novitiate until his death.
His penitential zeal rivalled that of the early anchorites, and, according to his spiritual director, he carried his baptismal innocence to the grave.
The chief work of Sanchez (and the only one that he himself edited) is the Disputationes de sancto matrimonii sacramento.
Even in the earlier editions of the Index as revised by Leo XIII, until his Constitution "Officorum ac munerum", there appears:
"This number is omitted from the edition of Venice, 1614; it treats of the power of the pope to grant a valid legitimation of the offspring of marriages invalid only through canon law through the so-called sanatio in radice.
These works also went through a series of different editions, and likewise drew upon themselves the accusation of laxity, especially with reference to the question of what is called "mental reservation" (restrictio mentalis).
One of them stated: If anyone, by himself, or before others, whether under examination or of his own accord, whether for amusement or for any other purpose, should swear that he has not done something which he has really done, having in mind something else which he has not done, or some way of doing it other than the way he employed, or anything else that is true: he does not lie nor perjure himself.According to Franz Xavier Wernz, Sanchez's work De matrimonio was reckoned by the Roman Curia among the classical works on marriage.