I get lots of questions about Galatians and how to interpret Paul’s words that even Peter found to be confusing at times. And to be honest, it can be easy to misconstrue one side of a conversation with only one letter. The key on Galatians 4 is that Paul is talking about an allegory. This is very important. And also he mentions 2 covenants.
All throughout the old and new testaments we hear mention of a 2nd Covenant or a New Covenant. I think people often misunderstand the covenants to be different in its terms. Covenant simply means an agreement or contract. The terms of the covenant were not to change. God does not change. (Mal 3:6) It was the person on our end of the agreement that was to change. The original signers (if you will) did not uphold their end of the covenant. So instead of them, it would go to their descendants after a long expulsion from the land.
I hope you enjoy the video.