This is the genitive form of the second person singular pronoun functioning as a possessive: 'your' or 'yours.' Greek regularly used the genitive case of personal pronouns to indicate possession rather than having separate possessive adjectives for all persons. So σοῦ or its enclitic form σου meant 'of you' or 'your,' appearing in contexts like 'your father,' 'your faith,' 'your house.' The form could be emphatic or enclitic depending on the emphasis needed. This grammatical feature made Greek pronouns highly efficient while maintaining clear distinctions between 'your' (singular) and 'your' (plural), a distinction lost in modern English.