Galatians 4  Paul continues to explain what it means to be an "heir".  A child is an heir to his father's estate.  As a child, he has no power to claim these things, for he is too young to manage them. In this way he is no different than a slave. However, that doesn't make him any less an owner. There will come a time in his life, when he is old enough, that he will be ready to take over the inheritance.

Likewise, there was a time when men were like children or slaves, under the rule of "the elemental things of the world." The Jews were slaves to the Law.  The Gentiles were slaves to false gods or philosophies. Neither of these were good.  Neither could justify or redeem. Both systems held people in bondage.  But, there came a time, "the fullness of time" when God sent His Son, under the Law, to fulfill the Law, and to redeem, set free all who were in bondage to the Law.  Likewise, those who were in bondage to false gods, could also be set free from slavery, when they came to believe in Jesus.  They also became sons of God, through Christ. 

The problem in Galatia was that those who had been set free from slavery to their false gods, now thought that they had to be slaves to the Law... the same thing that the Jews had been set free from!

We can almost hear Paul shouting, "No! No! NO!!! What are you thinking?"  No wonder he was perplexed about them.  Paul gives another example, another contrast to help them see the truth.
They all knew the story of Abraham and Sarah.  They knew that Abraham and Sarah were promised a child. And that they got impatient and chose to use Hagar as a surrogate and produced Ishmael.
Hagar is the bondwoman, a slave, and her son would not be an heir.  Sarah is the free woman, Abraham's wife, and her son Isaac would be free, the heir of all that Abraham possessed.

Paul says that those who are under the Law, or under a false god, are like Hagar.  They are in bondage and will inherit nothing.  But those who are children of the promise, like Isaac, are free, Sarah's children. These are the heirs.  " So then brethren, we are not children of a bondwoman but of a free woman."   We are sons and daughters, not slaves.  We are able to say "Abba Father " because we have been redeemed and adopted by the Lord God Himself, through faith in Christ Jesus. 

Abba Father, how can we thank You enough for the grace that You have given us?  We are Your children, Your sons and daughters, heirs of Abraham's blessings.   Lead us in Your ways and let Your perfect will be done.  May Your Kingdom come in all of its glory and everlasting perfection and peace.  Grant us today all our needs, our daily bread portions.  Forgive us our sins as we forgive others.  Lead us in paths of righteousness and truth and wisdom, away from temptations.  Deliver us from the darkness and lies and confusion of the evil one.  For You are God and all glory, honor, and power belongs to You.  Amen.