Christ did two things for those who were under the yoke of slavery (see Gal 5:1). First, He redeemed those under the Law. The Jews were enslaved to the whole Mosaic system. It was the bondage of legalism. Second, the incarnation, death and resurrection of Christ secured for all believers their birthright as sons and daughters: 

'Because you are sons, God sent the Spirit of his Son into our hearts, the Spirit who calls out "Abba, Father." So you are no longer a slave, but a son; and since you are a son, God has made you also made you an heir' (Gal 4:6-7). 

As believers we may not feel like children of God, but in reality we are. Our position in Christ is real truth, and we must choose to believe it.

The Holy Spirit resides in our hearts, ensuring our position in God’s family. The Spirit moves us to pray, 'Abba, Father.' The word 'Abba' is the Aramaic word for 'father.' It was used by small children who addressed their father. It would be similar to the English word 'Daddy.' 'Abba' implies intimacy and trust as opposed to slavery and legalism.

So you are no longer a slave, but a son; and since you are a son, God has also made you an heir. (Gal 4:7)

Thought for the Day: What does it mean to be an heir?

The Daily Discipler pp.112-113