Using the "armor of light”

[tadeus]

The Law of One blinks neither at the light or the darkness, but is available for service to others and service to self. However, service to others results in service to self, thus preserving and further harmonizing the distortions of those entities seeking intelligent infinity through these disciplines.

How do I understand this statement? 

STS is about separation, and STO is about all being one. Therefore, STO must include self, or there is separation.

...

To only serve others without serving the self is martyrdom and not an ideally balanced state.

STO must include the self, but not the service to self of others. There is an difference.

In this meaning the second sentence is correct, covering selflessness.

The logical conclusion is, that there can be no "armor of light”, if no differentiation is made to the (active) STS, because when every seperating is removed an armor can not exist and work.

Hopefully there is not another misunderstanding here, because the meaning of your next sentence is not clear?

Thus the STO being isn't giving anything away, so the choice to not be of service to STS beings may be seen more as a state of being rather than a one-off decision.

Your description of "the process of removing the boundary between self and others" is good and correct, i only want to point out the special case of STS beings, that want to active enslave and misuse you.