Behold, how great a love the Father has bestowed on us, that we should be called children of God! For this cause the world doesn't know us, because it didn't know him.

 In the New Testament there is the idea of adoption ( Romans 8:14-17; 1 Corinthians 1:9; Galatians 3:26-27; Galatians 4:6-7). Here is the idea that by a deliberate act of adoption on the part of God the Christian enters into his family. 