St. Ignatius Brianchaninov: after acquiring spiritual understanding...

It is worth noticing that, after acquiring spiritual understanding, the defects and faults of one’s neighbor begin to seem very slight and insignificant, as redeemed by the Savior and easily cured by repentance—those very faults and defects which seemed to the carnal understanding so big and serious. 

Evidently the carnal mind, being itself a plank, gives them this huge significance. The carnal mind sees in others sins that are not there at all.

St. Ignatius Brianchaninov