But when the time had fully come, God sent his Son, born of a woman, born under law, to redeem those under law, that we might receive the full rights of sons. 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 an heir.
Galatians 4 v 4–7
God sent His Son so that we can be His children. And He sends the Spirit of His Son so we can know in our hearts that we are His children.