Here in verse 3, the 1858 Wright edition replaced the definite article the in the phrase “cherubims and the flaming sword” with the indefinite a (“cherubims and a flaming sword”). The typesetter was probably influenced by the language found in the preceding verse (“cherubims and a flaming sword”), which is also the language of the King James Bible (see the discussion above under Alma 42:2). But since verse 2 has already mentioned the flaming sword, the use of the here in verse 3 is perfectly acceptable. The 1908 RLDS edition restored the correct the to the RLDS text.
Summary: Maintain in Alma 42:3 the definite article the in the phrase “cherubims and the flaming sword”, the reading of the original manuscript; the previous reference in verse 2 to the flaming sword allows the use of the definite article in verse 3.