Adoption

Adoption: Romans 8:15, "For you have not received a spirit of slavery leading to fear again, but you have received a spirit of adoption as sons by which we cry out, Abba! Father!"

The word adoption in the New Testament is translated from the Greek word (huiothesia) which means "the placing of an adult son" and refers to the formal act of recognizing the maturity of an adult son. The word is found in five New Testament passages: Rom. 8:15,23: 9:4; Gal. 4:5; Eph. 1:5.

When a believer is in union with Jesus Christ, this is  called (huios), "an adult son". So, when we are in union with Him, we are said to be adult sons .

 Positional advance is then the true meaning of "adoption", the  New Testament, "adoption" refers to a positional advance. The new believer is advanced positionally to his majority, even though at the time of salvation he is spiritually immature, a "babe in Christ".