Therefore you are no more a servant, but a son; and if a son, then an heir of God through Christ.
All Commentaries on Galatians 4:7 Go To Galatians 4
Ambrosiaster
AD 400
There is no doubt that one adopts a son in order to leave him an heir; but inheritance depends on the death of someone. How then can mortals be called the heirs of him who lives forever? The fact is that Scripture speaks in our own manner so that we may understand. In order to show that the Father will give from his goods those things that he is going to give his sons, it calls this “inheritance.”