This document seems to be a clarification of what is essentially Roman law.

It starts by stating the official position of the Catholic church. Even that translation is wrong (it should read that the Church, Christians and the Popes, past and present, pride themselves on having stamped out slavery everywhere they went). But litarally "Although the Roman Pontiffs have left nothing untried by which servitude be everywhere abolished among the nations, and although it is especially due to them that already for many ages no slaves are held among very many Christian peoples".

Then there is a sentence that should have made a world of difference in the translation of the rest of the document, which should be translated as "as long as we're NOT talking about slavery, here are clarifications about the laws concerning selling your labour/services to others in hopes of answering your questions". The word used is the same. That's because in Latin, as in the Roman empire, there is no concept of slavery. There are labour contracts and everyone providing their labour to someone else (always paid I might add, even in the cases we currently refer to as slavery). The point is, since there is no distinction in Latin between slave labor and non-slave labor, the text continues to use the word for laborer (servus, but keep in mind a slave is a servus, a cafe owner that serves you a drink is a servus, the guy you hire to redo your flooring is a servus).

Needless to say, a fair translation would have avoided the word slavery from that point forward. The English text doesn't. The text alludes to what makes something slave labor, and thus illegal : that the obligation of the laborer is either not limited in time, or wages are either not paid, or only paid in the sense that a debt is made whole (with the explicit exception of criminal debt).

It then states that one can sell one's labor, and that the resulting contract can be traded. It then keeps clarifying things about those contractual obligations, going on at length about the conditions that make labor relations non-slave labor. Firstly, there must be a time limit on the obligation (except in cases of conviction of a crime, ie. you can be convicted to serve for the rest of your life), and there must be payment, actual payment, "forgiving" a debt is not enough, although for instance valued instruction can be considered (partial) payment (in the Roman Republic and Empire it was common to train as a skilled profession (architect/doctor/lawyer/...) by training under someone, on the condition of serving as part of their company for a number of years. You still got paid, in addition to food, lodging, days off, ... but you could not start for yourself for the period specified. Initially this was limited by law to 2 years, eventually it became 20).

It then goes on that there are other conditions : no matter any contract, everyone has the right to marriage (and to not have the resulting family split up), the right to church and education (in the Christian faith, sure, but still), confession, humane treatment, ... And yes, such contracts can be enforced, even after selling/buying. There are strict conditions on the selling and buying of such labor contracts, and the penalty is always the same : if there is so much as reasonable suspicion that someone's being sold into slave labor, not only is the transaction null and void, but the labor contract itself (between the laborer and the boss) is null and void.

Did the American South abide by this letter ? Of course not.