Today we often freely refer to a Christian as a "son of God." However, I think it is very significant that we do not see the disciples called "sons of God" during the time Jesus was with them. Why not? What makes us sons of God?
During His ministry here on earth, Jesus most commonly referred to Himself as the "Son of man." However, others referred to Him as the "Son of God." "And the angel answered and said to her, 'The Holy Spirit will come upon you, and the power of the Highest will overshadow you; therefore, also, that Holy One who is to be born will be called the Son of God'" (Luke 1:35). "And John bore witness, saying, "I saw the Spirit descending from heaven like a dove, and He remained upon Him. I did not know Him, but He who sent me to baptize with water said to me, 'Upon whom you see the Spirit descending, and remaining on Him, this is He who baptizes with the Holy Spirit.' And I have seen and testified that this is the Son of God" (John 1:32-34).
Paul refers to Jesus as "the firstborn among many brethren." "For whom He foreknew, He also predestined to be conformed to the image of His Son, that He might be the firstborn among many brethren" (Rom. 8:29). In Hebrews we find the same language, with Christ referred to as our elder brother. "For it was fitting for Him, for whom are all things and by whom are all things, in bringing many sons to glory, to make the captain of their salvation perfect through sufferings. For both He who sanctifies and those who are being sanctified are all of one, for which reason He is not ashamed to call them brethren, saying: 'I will declare Your name to My brethren; In the midst of the assembly I will sing praise to You'" (Heb. 2:10-12). Is it really possible for us to be so closely related with God that we may be called "sons of God" and to refer to Jesus as "our brother"? If so, how is this accomplished?
Paul's letter to the Galatians is a statement of the gospel. The Galatians had begun well, but they had turned away and Paul is making a strong bid for them to turn back to the true gospel. "I marvel that you are turning away so soon from Him who called you in the grace of Christ, to a different gospel, which is not another; but there are some who trouble you and want to pervert the gospel of Christ. But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be accursed" (Gal. 1:6-8). It was not just a little error that had crept into their midst, but enough to completely destroy them. "You have become estranged from Christ, you who attempt to be justified by law; you have fallen from grace" (Gal. 5:4).
What was the gospel that Paul was declaring to them? We cannot discuss the entire letter to the Galatians, but we want to focus on the heart of it. Paul said that they had begun in the Spirit but were now trying to finish in the flesh. They were adding something to Jesus "just in case" Jesus was not enough. In so doing, they revealed that they were not really moving in faith, and thus not partaking of the grace of God that comes through faith in Jesus alone.
As Paul goes to the heart of the matter, I believe the following scripture is extremely important: "O foolish Galatians! Who has bewitched you that you should not obey the truth, before whose eyes Jesus Christ was clearly portrayed among you as crucified? This only I want to learn from you: Did you receive the Spirit by the works of the law, or by the hearing of faith?-- Are you so foolish? Having begun in the Spirit, are you now being made perfect by the flesh? Have you suffered so many things in vain--if indeed it was in vain? Therefore He who supplies the Spirit to you and works miracles among you, does He do it by the works of the law, or by the hearing of faith?" (Gal. 3:1-5)
Notice what Paul concentrates on. He talks about "receiving the Spirit" and "a supply of the Spirit" that is seen through supernatural manifestations. He says both come by "the hearing of faith." His argument is that the "works of the law" (what we can do on our own separate from God) do not produce this supply. Christ died to supply something that could come in no other way. Furthermore, he says that if it could come another way, the sacrifice of Christ was in vain (Gal. 2:21).
How then do we become sons of God? "For you are all sons of God through faith in Christ Jesus. For as many of you as were baptized into Christ have put on Christ" (Gal. 3:26-27). "But when the fullness of the time had come, God sent forth His Son, born of a woman, born under the law, to redeem those who were under the law, that we might receive the adoption as sons. And because you are sons, God has sent forth the Spirit of His Son into your hearts, crying out, 'Abba, Father!' Therefore you are no longer a slave but a son, and if a son, then an heir of God through Christ" (Gal. 4:4-7).
Brothers and sisters, I would say that this is the critical point. What does faith in Christ bring? Does not faith receive the Holy Spirit (God) into our lives? Is this not why Christ died? He died to open the way for God to indwell us by the Spirit. We are baptized in the Spirit into union with Christ. The indwelling Spirit takes us into fellowship with God and makes us a son of God in reality whereby we can know God as our "Daddy." Paul brings out the same truth in writing to the Romans. "For as many as are led by the Spirit of God, these are sons of God. For you did not receive the spirit of bondage again to fear, but you received the Spirit of adoption by whom we cry out, 'Abba, Father.' The Spirit Himself bears witness with our spirit that we are children of God" (Rom. 8:14-16). If this is presently not your understanding, I appeal to you to read the entire book of Galatians through carefully and ask God to reveal His mind regarding this great salvation.