What does Galatians 4:6 mean?

Paul continues to describe the amazing truth that those who come to Christ by faith are freed from slavery to the law, as well as to our own sinfulness, and are also adopted by God as His own children. Now Paul points to the Holy Spirit as the confirmation of this adoption.

God sends His Spirit to live in the hearts of every one of his adopted sons and daughters. The Holy Spirit is referred to here by Paul as the Spirit of His Son. He moves into our hearts and gives us the right, along with Jesus, to call out to God as a young child calls out to their "daddy." Abba means "father" in the Aramaic language. Because it's easy for young children to say, like the English term dada, it's what most young children would call their father. Without our own sinfulness and the law standing between us and God, we can live with God as little children do with a trusted father.

This verse helps to show how each member of the Trinity is involved in our salvation. God the Father sent the Son to save us, then sent the Spirit to live in our hearts.