“But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law, To redeem them that were under the law, that we might receive the adoption of sons.”
Christ paid the way for us, He made it possible for us to have Eternal Life through our belief in Him. Jesus Christ became our Passover Lamb and if you do not understand that, make sure you read the linked study.
We are naturally sons and daughters of our Father, He is our Creator. On a spiritual level however, we are not a part of His family unless we walk with Him and believe in Him. When we accept Christ into our heart and mind we become a part of our Father’s Family.
6 “And because ye are sons, God hath sent forth the Spirit of his Son into your hearts, crying, Abba, Father.”
This would be the Holy Spirit.
7 “Wherefore thou art no more a servant, but a son; and if a son, then an heir of God through Christ.”
When we accept Christ into our heart, mind and soul we become a part of that family and an heir of our Father’s Everlasting Kingdom.