The author makes the case that Christianity should leave some very 'positive' evidences on those who profess to have it, and so it should.
The author blames a diluted gospel for the lack of 'spiritual evidences' in the lives of many who profess Christ, yet there are many serious Christians who struggle.
The author propagates 'works' (mostly difficulties) as the way to attain spiritual maturity, which is just as bad as 'too much grace'.
People are 'saved by grace through faith', the initial work (grace) is accomplished by God. Obviously whatever God does is good so it has to be whatever is coming afterwards (the teachings of men) that is causing all the problems.