62 This same doctrine was again solemnly repeated and confirmed by the Church in the condemnation of the Jansenist heresy which dared to utter this blasphemy against the goodness of God: "Some precepts of God are, when one considers the powers which man possesses, impossible of fulfillment even to the just who wish to keep the law and strive to do so; grace is lacking whereby these laws could be fulfilled."
Source: Casti Connubii (Vatican.va)