Nietzche’s general project in the “The Genealogy of Morals” is to provide a historical account of morality. He doesn’t explicitly aim to offer any prescriptions, but rather chooses to provide his account on the manner in which we have come to arrive at morality as it is today.
There are two principle kinds of morality that Nietzche analyzes in the first essay of The Genealogy of Morals. They are the master morality and slave morality.
For Nietzche, the master morality is represented by the values of the individuals who actually exert (what he believes to be) human being’s inherent will to power. In this form of morality, the individuals first establish themselves as good, and then establish that the people who aren’t like them as bad, as an afterthought. He notes that the Greeks referred to their servants and slaves in a fashion that radiated their obvious belief that their slaves were insignificant creatures.
The slave morality is represented by the values of the individuals who bear the negative effects of “the masters” exercising their will to power. The slave morality is typified by first establishing that whatever is good to the individuals of the master morality is evil for the slave morality. After that, the individuals of the slave morality establish that everyone who isn’t like the individuals represented by the master moralist, as good.
Observe that the slave morality characterizes the “good” of the master morality as evil whereas the master morality characterizes the “good” of the slave morality as simply bad. So it should be evident that the slave morality is reactionary to the expression of the will to power.
There is larger significance to Nietzche’s analogy. One must note that even though Nietzche might admit that ancient societies were much more brutal, he would still assert that the members of those societies were more cheerful than members of today’s society. This is because individuals from those times expressed their inherent will to power. Nietzche provides the example of a member from today’s society reading the book “Don Quixote” with an astonishment at the level of brutality in the book. However the writer of the book and his contemporaries probably found the contents quite normal and natural.
At this point it is important to highlight that for Nietzche, the slave morality (characterized by “ressentimente”) is what led to the establishment of religion and other such social institutions. This is because the suppressed expression of the will power leads to the “internalization of man” causing man to develop a soul. Nietzche also thinks that the slave morality would result in individuals who are much more cunning or intelligent as it seeks to justify the denial of human being’s inherent will to power. This would cause individuals to invest heavily in thought. So for Nietzche, such an evolution of morality based on this analogy of the slave and master morality, is the primary reason why contemporary society is insipid and dull.