I am a sinful man. True conviction has regard to what one is, not to what one has done. Compare Manoah (Jdg_13:22), Israel (Exo_20:19), men of Beth-shemesh (1Sa_6:20), David (2Sa_12:13), Job (Job_40:4; Job_42:2-6), Isaiah (Isa_6:5).
a sinful man = a man (App-123.) a sinner. Emphasizing the individual.