The priest told him that sincere repentance could cleanse his transgressions.

transgressions 是名词 transgression 的复数形式。transgression 由前缀 trans-（表示"跨越"）和词根 gress（表示"行走"）组成，字面意思是"越界行为"，引申为"违反道德或宗教戒律的行为"，即"罪过"。