The kingdom of self

Many people not only lose the benefit, but are even
the worse for their mortifications [i.e., sacrifices,
abstensions]. It is because they mistake the whole
nature and worth of them. They practice them for their
own sakes, as things good in themselves; they think them
to be real parts of holiness, and so rest in them, and
look no further, but grow full of a self-esteem, and
self-admiration for their own progress in them. This
makes them self-sufficient, morose, severe judges of all
those that fall short of their mortifications. And thus
their self-denials do only that for them, which indulgences
do for other people--they withstand and hinder the
operation of God upon their souls; and instead of being
really self-denials, they strengthen and keep up the
kingdom of self.
- William Law (1686-1761), "The Spirit of Prayer"