Considering the cultural context of ancient Israel, what was the primary societal function of the 'goel' (kinsman-redeemer), as exemplified in the book of Ruth?

A To primarily serve as a religious leader, interpreting the Law for the community. B To primarily oversee agricultural practices and ensure fair distribution of land. C To primarily act as a military protector, defending the family from external threats. D To primarily preserve the family line by marrying a widow of a deceased relative and redeeming lost property.