The 1830 typesetter accidentally omitted the repeated definite article the in the conjunctive noun phrase “and all the preaching and the prophesying”. The use of the repeated determiner is characteristic of the Book of Mormon text. In accord with the earliest extant source (the printer’s manuscript), the critical text will restore the original repeated the here in Helaman 6:2.
Summary: Restore in Helaman 6:2 the original repeated the in “all the preaching and the prophesying”, the reading in 𝓟 (here the earliest extant source).