The Book of Galatians was one of Paul's letters to several churches in Galatia, written about A.D. 48. A Jewish element in these churches taught that one must be obedient to the law of Moses and the Gospel to be saved.
This book refutes that idea. There are three main elements to Paul's argument to the Galatian churches.
First, there is a defense of his apostleship, thus, his authority (1-2).
Second, there is the proposition that the law served a temporal, preparatory function. It was abolished, therefore, by the completion of Christ's mission (3-4).
Finally, one must personally accept one's responsibility to avoid the works of the flesh and to pursue the development of the Spirit's fruit (5-6).