"We are of all men most miserable" means Christians are the gloomiest, unhappiest people around

1 Corinthians 15:19 reads, "If in this life only we have hope in Christ, we are of all men most miserable." Paul's argument is that if there's no resurrection, then Christians who've given up worldly advantage for a false hope are the most pitiable people alive, not that they walk around feeling sad. "Miserable" here comes straight from Latin "miserabilis," "to be pitied," the same root as "misery" and "commiserate."

Modern English kept the subjective, feelings-based sense of "miserable" (personally unhappy) and largely dropped the older, more objective sense (an outside observer's judgment that you're to be pitied), so readers assume Paul is describing an emotional state rather than a status.