What is the meaning of the prohibition of ribā in sales being a prohibition of means, and the prohibition of ribā in debts being a prohibition of ends?

The meaning of this phrase is that riba (usury/interest) on debts is the basis for the prohibition of riba, encompassing both increase (ziyadah) and deferment (ta'jil), whereas riba on sales might be limited to one of them and only occurs in usurious commodities. The prohibition of riba on sales is not merely to block pretexts (sadd al-dhara'i'); rather, it was established by sacred texts that described it as riba itself, such as the hadith of Abu Sa'id al-Khudri concerning the exchange of dates, and similar to the prohibition of selling after the call to Jumu'ah prayer due to the pretext of being distracted from prayer and the sermon, as in His (Allah's) saying: "O you who have believed, when [the adhan is] called for the prayer on the day of Jumu'ah, then proceed to the remembrance of Allah and leave trade."