The typesetter for the 1841 British edition accidentally set the as to be, a perseverance of the immediately preceding to be in “God ceaseth not to be God”. What is rather surprising here is that this typo was copied into the subsequent 1849 LDS edition. The 1852 LDS edition restored the original the to the LDS text.
Summary: Maintain in Alma 42:23 the original text for the clause “and mercy claimeth the penitent”.