Galatians 4: The Creator is the "Papa/Father" to those who has Jesus.

 Paul said to the Galatians:
4-7 But when the time arrived that was set by God the Father, God sent his Son, born among us of a woman, born under the conditions of the law so that he might redeem those of us who have been kidnapped by the law. Thus we have been set free to experience our rightful heritage. You can tell for sure that you are now fully adopted as his own children because God sent the Spirit of his Son into our lives crying out, “Papa! Father!” Doesn’t that privilege of intimate conversation with God make it plain that you are not a slave, but a child? And if you are a child, you’re also an heir, with complete access to the inheritance.

Paul said that the Galatians were kidnapped by the Law, but Jesus came to redeem them; so they don't have to (or must not to) apply the ceremonial law (make the circumcision) to them. They became children of the Lord, and they now have the Spirit of Jesus into their lives crying "Papa!" to the Lord.
Paul remembers how the Galatians were friendly to him, but now, due to the Judaizers, he feels that their relations is colder. He said that the Judaizers want them to become slaves when in fact they were the slaves (of the Law).