Roman adoption was essential for those families with no male heirs. The family estate always passed down through the male line.
A man of wealth would go through a legal procedure to adopt a male heir from a poor family, thus guaranteeing that young man’s new and abundant future.
The adopted son became as much a part of the family, as much of an heir, as any others that might come before or after him. Like Co-heirs with Christ, the scripture says.
Until their full inheritance was realised, all their income and all they owned belonged legally to the head of the household. He then allowed his adopted son and the son’s household to share some of that wealth for their own use and comfort.
That’s how the writer to the Romans of the day wanted us all to understand our relationship with Father God. There is nothing we don’t owe him and every good thing we children have comes from him.
