The contrast presented between verses 12 and 13 show the extreme differences of those who had been baptized. Those noted in verse 12 are reverting to their non-Christian-covenant ways of social stratification, and ignoring those in need to dwell on their own wealth. Those noted in verse 13 are those who are not only baptized, but who follow the covenant to Christ to be egalitarian and care and feed those in need. These are the ones who follow the covenant made under Benjamin.
Mormon clearly notes that these people are doing these things as part of their covenant. This is very specifically done “for Christ’s sake, who should come…” These are those who believe in the coming Atoning Messiah.