Here "faithful" means to do what God commands one to do. You can state this clearly. AT: "to those who faithfully obey your commandments" or "to those who faithfully do your covenant" (See: [[rc://en/ta/man/translate/figs-explicit]])
# to a man who is blameless ... you show yourself pure
Both of these clauses have similar meanings. The writer repeats these ideas for emphasis. (See: [[rc://en/ta/man/translate/figs-parallelism]])