"And there was a thick darkness throughout the land of Egypt... No man could see his brother nor could any man rise from his place" [Bo 10:22-23]
This verse, said R' Chanoch of Alexander, teaches us a valuable lesson in Divine service.
''And there was a thick darkness throughout the land of Egypt'' - when it is a period of spiritual darkness - and ''No man could see his brother'' - when somebody only cares about himself and ignores the plight of others - then ''nor could any man rise from his place'' - he will not be able to rise from his low spiritual state.
Source: Rabbi Yisrael Bronstein