When you receive Jesus Christ, you become a child of God, and you also receive the “Jesus nature,” a nature that knows to call God the Father “Daddy.” This is a very natural relationship.
In Romans 8, Paul addressed two major subjects—birth and adoption. Do not confuse them; they are distinctly different. Birth produces a nature; adoption gives a legal standing.
God is so good to us that we get it both ways—birth and adoption—but they don’t give us the same thing. We receive something distinct by each process.
This is perfectly understandable in the light of the customs of the Roman Empire. In Paul’s day, it was not uncommon for the Roman emperor to have many sons, but when he chose one particular son to succeed him as emperor, he would also adopt that son. Then, all the legal rights of the empire would go to that adopted son. The purpose of adoption was legal—it assured the son’s inheritance.
We are born again at regeneration, and we receive the “Jesus nature.” But, at the baptism in the Holy Spirit, we receive adoption. Heaven’s best Lawyer comes in and assures us that we are the children of God. This is what assures us of the inheritance we receive. Do you see the implication?
It is just like the Roman emperor. If he has a son by natural birth, his son gets his nature. But in order to receive the inheritance, that son needs to be adopted; this gives him a legal standing and rightful inheritance.