Carl Trueman's recommendation in a recent Themelios was the final motivation I needed to pick up Christianity and Liberalism, Machen's plea for self-describing Christians to recognize the worlds-apart difference between (supernatural) Christianity and (de-supernaturalized) Liberalism/Modernism. Read it on a plane to and from Mexico and, though I would certainly not call it the second most important book a theological student could read, I loved it. Now I'm working through Ned Stonehouse's biography, the style of writing of which is not my taste, but is opening up Machen to me as, of course, no one else would be able to do (Stonehouse was a student and then colleague of Machen's at Westminster).
Here are a few of my favorite quotes.
[T]he things that are sometimes thought to be hardest to defend are also the things that are most worth defending. (8)
Indifferentism about doctrine makes no heroes of the faith. (51)
Human affection, apparently so simple, is really just bristling with dogma. (55)
Christian experience is rightly used when it helps to convince us that the events narrated in the New Testament actually did occur; but it can never enable us to be Christians whether the events occurred or not. (72)
When we come to see that it was no mere man who suffered on Calvary but the Lord of Glory, then we shall be willing to say that one drop of the precious blood of Jesus is of more value, for our salvation and for the hope of society, than all the rivers of blood that have flowed upon the battlefields of history. (128)
And finally, a statement that stands in direct contrast to some recent Christians writers emphasizing the love of God to neglect of God's wrath:
Religion cannot be made joyful simply by looking on the bright side of God. For a one-sided God is not a real God, and it is the real God alone who can satisfy the longing of our soul. (134)