"I am amazed that you are so quickly deserting Him who called you by the grace of Christ, for a different Gospel; which is really not another; only there are some who are disturbing you and want to distort the Gospel of Christ." Galatians 1:6-7
What an amazing passage. Brethren were unknowingly leaving their heavenly Father by receiving another Gospel. Paul gave further warning saying that even if an angel from heaven should bring a different Gospel that he is to be doubly cursed!.
So, what was the distorted Gospel that the Galatians were receiving? Certain men from Jerusalem had come and told the Galatians that they must be circumcised and keep the whole Law of Moses in order for their salvation to be complete. These men were teaching salvation by works rather that salvation by grace through faith which the Apostle Paul had taught them. But Paul assured them that he had gone to Jerusalem and presented his Gospel to the Apostles and that they added nothing to him.
Later in his letter Paul explains that to go back to physical circumcision and the observance of the Book of the Law would be to leave Abrahamís Covenant of Promise for the Sinai Covenant of bondage. Paul explains that there are two Covenants, one associated with the Book of the Law, Jerusalem, Hagar and bondage, this is the Sinai Covenant which contained laws added because of transgressions - and one associated with the Ten Commandments, New Jerusalem, Abraham, Sarah and freedom, this is the Christian Covenant of Promise. In Chapter five, Paul warns that if a man receives circumcision then he is obligated to keep the "whole" law and has been severed from Christ.
Since the Bible teaches Christians to observe Godís Laws, what does Paul mean when he writes "whole law?" And why would he be taking such issue over observing the Law when he said that "what matters is keeping the Commandments of God?" (1 Cor.7) It really is more about the Covenants than the Law. Abrahamís Covenant of Promise is the Christian Covenant which is why the saints are called "Abrahamís offspring", "true circumcision" and "Israel of God." God offered Abrahamís Covenant to Israel in the wilderness of Sinai but they did not enter. As a result God offered them a temporary Covenant containing additional Laws added because of transgressions to preserve them until the Promised Seed, which is Jesus, would come. On the day of Pentecost 31 AD God again offered Israel the Covenant of Promise and 3000 entered into it that day. Later it was expanded to the Gentiles who become Abrahamís children as they are born again of the spirit. To enter into this covenant, is to enter into the real which promises eternal life.