A person engaged in spiritual work is not allowed to eternalize an egoistic reality. It is temporary. You exit this reality and it does not exist; it must burn out!
In this case we are talking about the fact that you have no right to use the skin as a monument of your states. By doing so you seemingly stop your movement, you do not want to go beyond the highest egoistic substance.
Nowadays, tattoos on the body have become very popular. We are in the final stage of egoistical development where a person is attracted to tattoos, but they are a reflection of the intrinsic properties that we need to go through to get in to the upper world.