In today’s study we see how that we are now the sons of God because God has sent forth the Spirit of his Son into our hearts. Therefore, we are no longer servants, but heirs through Christ. Specifically, Paul is addressing Galatians Gentile believers that made up the Body of Christ; both Jew and Gentile of which we are a part of today.
Verse 6: And because ye are sons, God hath sent forth the Spirit of his Son into your hearts, crying, Abba, Father. Now Paul makes another switch from we in verse 5 to ye and is still speaking directly to the Galatian believers (i.e., the Body of Christ made up on both Jew and Gentile). By faith, they have been brought into a sonship relationship by the giving of the Spirit of his Son in which they too can now cry out Abba, Father.
Verse 7: Wherefore thou art no more a servant, but a son; and if a son, then an heir of God through Christ. Interestingly, Paul now switches to first person singular. I have come to believe that he is addressing the servant in verse 1 who would eventually have Israel as their Lord has now become equal with Israel as joint heirs.
Again, for clarification, this does not mean that we, the Body of Christ, obtain Israel's earthly promises. However, we do become joint heirs with those Jews who are now a part of the Body of Christ in heavenly places.
Verse 8: Howbeit then, when ye knew not God, ye did service unto them which by nature are no gods. This verse is squarely directed at the Gentile believers still who had been misled by the Judaizers regarding the law. I don't think the Gentile believers necessarily believed they had to "go back" to the Mosaic law, because they were never under it, but instead were being led to believe they had to obey it to be saved.
Verse 9: But now, after that ye have known God, or rather are known of God, how turn ye again to the weak and beggarly elements, whereunto ye desire again to be in bondage? We have already established that the Gentile believers were never under the Mosaic law, therefore, whereunto ye desire again to be in bondage cannot be referring to that. Instead, I believe when he asks how turn ye again to the weak and beggarly elements, he is referring to the bondage of their paganism. Either way, the Judaizers would have been promoting the law of Moses which was also bondage.