Pharisaism and Christianity by Hugo Odeberg, translated from the Swedish "Fariseism och kristendom" by John M. Moe, published by Concordia Publishing House in 1964. This excerpt comes from pages 14-15.
Another way of approaching the difference between Christianity and Pharisaism is the following. It is admitted that this antithesis does in fact exist. The fundamental Christian principles are emphasized and an attempt is made to define them precisely. Thereupon an ethical and a religious view is constructed which forms the direct opposite of the Christian view which has just been defined and the conclusion is drawn that this is precisely what the Pharisaic view must have been, since Pharisaism was the antithesis of Christianity. However, the Pharisaism thus constructed is shown, upon closer examination, to be the very opposite of Pharisaism. Here we really deal with a case entirely analogous to the one described earlier. What is depicted as Christianity is not Christianity but Pharisaism.
How are we to account for this? Clearly by the fact that the Pharisaical ways of thinking have become natural for us without our being aware that they are Pharisaical. And what appears to us natural and reasonable is assumed — if one highly esteems the name of Christianity — as something self-evident in Christianity. We cannot and will not suppose — if we regard Christianity as the supreme religion — that the ideals set up by Christianity can be different from those we set up as the reasonable and the best. The only error is that these ideals have not derived from Christianity but from Christianity’s antithesis: from Pharisaism. The result is that we confuse Christianity with Pharisaism and, while professing to be Christians, actually espouse Pharisaism.
The only proper method of establishing the true difference between Christianity and Pharisaism is obviously that we seek to obtain as accurate a knowledge of both as we possibly can, and it is especially important that we gain a correct knowledge of the doctrines and fundamental principles of Pharisaism. A true knowledge of Pharisaism is of fundamental importance for the protection of the unique character of Christianity.