The word "teknon" means "child" and the word "huios" means "son". A son is one who is mature and is considered able to take over responsibility in the household.
There are at least five aspects of adoption:
1. Right to be called the children (teknon) of God (John 1:12). Those who receive Jesus into their life are granted the right to be called the children of God. In other words, all legal indictments against them are cancelled and they have a legal position as God's children. This is what Jesus procured for us on the cross.
2. Spirit of adoption sent into hearts of believers (Romans 8:14, 15,16). The Spirit bears witness with our spirit that we are the children (teknon) of God. Those who obey the leading of the Spirit are the sons (huios) of God.
3. We are being conformed to the image of the Son (Romans 8:29). Through the Spirit we are being transformed in conformity to the image of the Son (2 Corinthians 3:18). This refers to the process of spiritual growth into the likeness of Christ (Ephesians 4: 13,14).
4. The manifestation of the sons of God (Romans 8:19-23). This is also known as the "glorious liberty of the children (teknon) of God", "the redemption of our body", and "the revealing of the sons (huios) of God". This is prospective and will happen at the end of the age. At the coming of Christ, this mortal body will put on immortality and will be transformed into the likeness of the body of Christ (Philippians 3:21; 1 John 3:2; 1 Corinthians 15:46-54)
5. Rule with the rod of iron (Revelation 2:26-28). The one who overcomes will rule with Christ and have power over the nations in the coming Kingdom.