The abstract noun "faith" can be stated as the verb "believes." There are also words that Paul left out, but they are understood. Alternate translation: "So a person believes in Christ by hearing the message about Christ (See: rc://en/ta/man/translate/figs-abstractnouns and rc://en/ta/man/translate/figs-ellipsis)
Here "word" is a metonym that means "message." There are also words that Paul left out, but they are understood. Alternate translation: "and a person hears the message by someone preaching the message about Christ" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-ellipsis)