Usbek to Rhedi in Venice
Libertines maintain an infinite number of trollops here, and the pious an innumerable number of dervishes. These dervishes take three vows : obedience, poverty, and chastity. They say that the first is the best observed of all ; as for the second, I can tell you that it is not ; I will let you be judge of the third.
But however rich these dervishes are, they never relinquish the quality of poor ; our glorious sultan would sooner renounce his magnificent and sublime titles. They are right, for this label prevents them from being poor.
Physicians and some of these dervishes they call confessors are always too highly thought of or too looked down on, yet they say that heirs find physicians more to their liking than confessors. 
The other day I was in a convent of these dervishes. One of them, venerable for his white hair, welcomed me most civilly, and after showing me around the whole house, he took me into the garden, were we began to talk. Father, I said to him, what is your function in the community ? Monsieur, he replied, seeming very pleased with my question, I am a casuist.  Casuist ? I repeated. In all the time I have been in France, I have never heard of this function. What ? You don’t know what a casuist is ! Well, listen : I am going to give you a notion of it that will leave you nothing to desire. There are two sorts of sins : mortal sins, which absolutely exclude a person from paradise ; and venial sins, which do, in truth, offend God, but do not anger him to the point of depriving us of beatitude.  Now our whole art consists in properly distinguishing these two sorts of sins : for with exception of a few libertines,  all Christians want to enter paradise ; but there is hardly anyone who doesn’t want to enter there as cheaply as it can be done. When you are well acquainted with mortal sins, you try to commit any of those, and your make your deal. There are men who do not aspire to such great perfection, and as they have no ambition, they do not worry about the principal ranks ; so they just barely get into paradise : as long as they get in, that is all they ask  ; their goal is to do no more nor less than necessary. Those are people who rather steal heaven than obtain it, and who say to God : Lord, I have strictly fulfilled the conditions ; you cannot help but keep your promises ; as I have done no more than you required, I dispense you from granting me more than you promised.
We are therefore necessary men, monsieur. Yet that is not all : you are going to see more. The crime is not in the act, but in the knowledge of the person who commits it, He who does something wrong while he can believe that it is not wrong, est secure in his conscience ; and as there are an infinite number of equivocal acts, a casuist can give them a degree of goodness that they do not have by qualifying them as such ; and provided he can persuade that there is no venom in them, he removes it entirely.
I am telling you here the secret of a profession in which I have grown old ; I am showing you its refinements : there is a turn to give to everything, even to things that seem the susceptible of it.  Father, I said, all well and good ; but how do you come to terms with heaven ? If the great sophi had a man like you in his court, who did with respect to him what you do against your God, who made distinctions among his orders, and taught his subjects in which case they must execute them, and in what other case they can violate them, he would have him empaled on the spot. Thereupon I excused myself to my dervish, and left him without awaiting his reply.
Paris this 23rd day of the moon of Maharram 1714