How does the Apostle Paul utilize the concept of 'adoption' in his letters (e.g., Romans 8:15, Galatians 4:5) to describe the relationship between believers and God?

A Adoption is used to emphasize the legalistic requirements for becoming a Christian. B Adoption is used primarily to illustrate the financial benefits of following Christ. C Adoption illustrates the intimate, familial relationship believers have with God as His children, inheriting the rights and privileges of sonship. D Adoption serves as a metaphor for the temporary nature of our relationship with God.