Here are some snippets from Machen's Notes on Galatians [For US readers the Westminster Bookstore has it here]. The newsclipping is from the PCA Historical Centre.
The Epistle to the Galatians is a polemic, a fighting Epistle from beginning to end. (p. 8)
All definition is by way of exclusion. You cannot possibly say clearly what a thing is without contrasting it with what it is not. When that fundamental law is violated, we find nothing but a fog. (p. 6)
The first word of the Epistle, after the address is over, is not "I gave thanks" but "I am surprised": Paul plunges at once into the matter that caused the Epistle to be written. "You are turning away from the gospel," he says in effect, "and I am writing this Epistle to stop you."
What is the reason for this absence, in the Epistle to the Galatians, of the usual thanksgiving? The answer is really very simple. Paul omitted giving thanks, for the simple reason that there was nothing to be thankful for. (p. 34)
Thanksgiving at such a moment would have been blasphemy; praise of the Galatians would have been cruelty. Paul engaged neither in thanksgiving nor in praise. Instead, he wrote this mighty Epistle, with its solemn warning, with its flaming appeal. (p. 35)