In most instances, therefore begins sentences in the Book of Mormon text, but there are 18 cases where the therefore is preceded by the conjunction and. Here in 𝓞 for Alma 59:10, Oliver initially wrote “& therefore”, but then he crossed out the ampersand. There is one other case where Oliver Cowdery accidentally added an and before therefore in the text, but again only momentarily:
For each instance of therefore, the critical text will follow the earliest extant reading, thus therefore without a preceding and in Alma 59:10.
Summary: Maintain in Alma 59:10 the corrected reading in 𝓞, therefore without any preceding and.