What does the word adoption really mean for a believer?

Les teaches that in the culture of the text, when a son reached the age and was ready for his position with the father, they went through the rites of adoption. The word really means the person is placed as a full son—not just as one born into the family, not as one legally taken from another family, but as a son who has gone through the training years, been prepared and tutored, and is now placed as a full partner with the Father. The glory is that at salvation we are born into the family of God by the work of the Holy Spirit, and immediately God also places us as the full heir with Jesus Christ. We do not have to work for twenty years like Jacob did, nor strive and strain hoping to attain this position; it happens the moment we believe, so we can say Abba Father. The passage goes on to say that if we are children, then we are heirs—not just an heir down the line hoping for a little inheritance, but joint heirs. In our own culture, a joint heir implies equality: what is His is hers, and vice versa.