Just Because

The oblique cases of the Pers. pron. appear in the form of suffixes to nouns, verbs, and particles. (a) Suffixes to nouns are in gen., and are equivalent to our possessive pron. Gen. 4:1 אִשְׁתּוֹ his wife, 4:10 אָחִיךָ thy brother. This gen. is usually gen. of subj., as above, but may be gen. of obj., Gen. 16:5 חֲמָמִי my wrong (that done me). 18:21.*

*A. B. Davidson, Introductory Hebrew Grammar Hebrew Syntax, 3d ed. (Edinburgh: T&T Clark, 1902), 2.