French Jesuit Blessed Peter Favre: On Dealing With Heretics

'Since one of the commonest errors of the Lutherans is the ascribing merit to faith alone, denying it altogether to good works, the right way to proceed in the matter of their conversion is to begin by exciting them to the performance of good works, and to come to the question of faith afterwards.

Thus, when a heretic denies the Church's power to make the hearing Mass or reciting the divine office an obligation under pain of grievous sin, we should strive to bring him to practice these and other pious exercises, because he abandoned them before forsaking the faith.

Besides this, we should remember what is the principal prop on which these leaders and teachers
of heresy rely in maintaining their errors, in opposition to the precepts of the Church and the rules of the holy Fathers.

They say that they have not sufficient strength to obey God, and that the Church's laws and precepts are intolerable to human nature.

They ought, therefore, to be encouraged to trust in God with all the energy of their minds, and so to make themselves capable, by His help and grace, not only of keeping the precepts, but of advancing to greater and more perfect things.

Link (here) to the book entitled, "The life of Blessed Peter Favre of the Society of Jesus, first companion of St. Ignatius Loyola"

More on Bl. Peter Favre (here) (here) and (here)