Sublimis Deus answers a question that had been argued in Spain for a generation: whether the peoples of the Americas were rational beings capable of faith and of holding property, or whether they were natural slaves in the Aristotelian sense, fit only to be governed by others. Paul III answers plainly. They are true men. They are capable of understanding the Catholic faith and are, in the pope's words, exceedingly desirous to receive it. Therefore they are not to be deprived of their liberty or the possession of their property, even if they remain outside the faith, and anything done to the contrary is null and of no effect.
The bull is short and its scope is wide. It covers not only the peoples already encountered but any others who might later come to the notice of Christians, which is unusual drafting for the period and was probably deliberate.
What it does not do is repeal anything. Inter Caetera stood. The encomienda stood. The bull addresses the treatment of persons, not the title to territory, and the two questions were kept carefully apart. Read next to the 1452 and 1455 grants it is a genuine reversal on slavery and an eloquent silence on conquest, and the atlas records both halves of that.