Athanasius of Alexandria

In his own words on Galatians

• Galatians 2:20

  Christ is the true Son, and so when we receive the Spirit, we are made sons. For it says; 'you did not receive the spirit of slavery leading you back into fear, but you have received the Spirit of adopted sonship' [Romans 8:15]. But when we are made sons in the Spirit, it is clear that we are called children of God in Christ... And when the Spirit is given to us-the Saviour said: 'Receive the Holy Spirit' [John 20:22]- God [The Father] is in us... But when God is in us, the Son is also in us. For the Lord Himself said: 'I and the Father will come and make our home with him' [John 14:23]. Next, the Son is life-for He said: 'I am the life' [John 14:6]- and so we are said to be given life in the Spirit... But when we are given life in the Spirit, Christ Himself is said to live in us. For it says: 'I am crucified with Christ. It is no longer I who live, but Christ who lives in me.' (Galatians 2:19-20). - "Letters to Separion On the Spirit, Letter 1, Chapter 19"

• Galatians 4:6

  But this is God's kindness to man, that of whom He is Maker, of them according to grace He afterwards becomes Father also; becomes, that is, when men, His creatures, receive into their hearts, as the Apostle says, 'the Spirit of His Son, crying, Abba, Father.' And these are they who, having received the Word, gained power from Him to become sons of God; for they could not become sons, being by nature creatures, otherwise than by receiving the Spirit of the natural and true Son. Wherefore, that this might be, 'The Word became flesh,' that He might make man capable of Godhead. This same meaning may be gained also from the Prophet Malachi, who says, 'Hath not One God created us? Have we not all one Father?' for first he puts 'created,' next 'Father,' to shew, as the other writers, that from the beginning we were creatures by nature, and God is our Creator through the Word; but afterwards we were made sons, and thenceforward God the Creator becomes our Father also. Therefore 'Father' is proper to the Son; and not 'creature,' but 'Son' is proper to the Father. Accordingly this passage also proves, that we are not sons by nature, but the Son who is in us; and again, that God is not our Father by nature, but of that Word in us, in whom and because of whom we 'cry, Abba, Father.' And so in like manner, the Father calls them sons in whomsoever He sees His own Son, and says, 'I begat;' since begetting is significant of a Son, and making is indicative of the works. And thus it is that we are not begotten first, but made; for it is written, 'Let Us make man;' but afterwards, on receiving the grace of the Spirit, we are said thenceforth to be begotten also; just as the great Moses in his Song with an apposite meaning says first 'He bought,' and afterwards 'He begat;' lest, hearing 'He begat,' they might forget their own original nature; but that they might know that from the beginning they are creatures, but when according to grace they are said to be begotten, as sons, still no less than before are men works according to nature.

  Four Discourses Against the Arians, Discourse 2, Section 59