The 1906 LDS large-print edition added a second connective element here before the sentenceinitial therefore, namely and. This edition was never used as a copytext for subsequent LDS editions; thus the intrusive and was restricted to that edition. Either reading is, of course, possible. Most of the time therefore is not preceded by any other connective element, but there are 18 occurrences in the text of and therefore. Here in Alma 19:32, the critical text will maintain the earliest text without the and.
Summary: Maintain the earliest text in Alma 19:32: namely, the therefore without any preceding and.