Plen (πλήν) is an adversative conjunction or adverb meaning but, however, nevertheless, only, or except. It introduces a contrast, limitation, or exception. Stronger than de, it often marks a significant turn in argument.
Jesus uses plen at critical turning points. In Luke 6:24, after the Beatitudes He turns sharply: 'But woe to you who are rich.' In Luke 22:22, He announces betrayal: 'The Son of Man will go as decreed. But woe to that man who betrays him!' — holding divine sovereignty and human responsibility together. In Luke 10:20, He redirects joy: 'However, rejoice that your names are written in heaven.' Each use recalibrates priorities and redirects attention to what truly matters.