The last part of this passage (“to those priests that stood in need / yea and to every needy naked soul”) was accidentally omitted when Oliver Cowdery initially copied this part of the text from 𝓞 into 𝓟. This error probably resulted from his eye skipping down a whole line in the original manuscript. There are two other examples of this kind of lengthy visual skip in this part of the text (in Mosiah 17:2 and Mosiah 18:35). In all three cases, there do not appear to be any identical words or phrases that could have led to the visual skip. Here in Mosiah 18:28, Oliver supralinearly inserted the long line of text at some later time, probably when he proofed 𝓟 against 𝓞 (the level of ink flow is somewhat heavier).
The 1830 compositor, as he was adding punctuation in pencil to the printer’s manuscript (just prior to setting the type), apparently felt that there was a missing conjunction at the beginning of this line of text that had earlier been skipped, so he inserted an ampersand in pencil at the beginning of Oliver Cowdery’s long supralinear insertion. Yet this inserted and makes little sense. The and leads the reader to think that the people’s “good desires” were not only “towards God” but also “to those priests that stood in need” and “to every needy naked soul”. Although the people would have had such desires, the actual intended meaning is that the people “should impart of their substance ... to those priests that stood in need / yea and to every needy naked soul”. The long prepositional phrase “of their own free will and good desires towards God” describes the source of the people’s charity.
Summary: In Mosiah 18:28 the critical text will follow Oliver Cowdery’s corrected reading in 𝓟 (with its restoration of a full line of 𝓞); on the other hand, the secondary (and misleading) and that the 1830 compositor added will be removed.