Paul refers to the Mosaic law.1 It is likely that some of the Judaizers were claiming that Mosaic law supplemented and defined the Abrahamic covenant.2 Paul makes it clear that this is not the case. The covenant with Abraham takes precedence over the covenant made through Moses since it came first.3 The agreement with Abraham is not annulled or changed by the agreement made through Moses.4
17 This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void.