rendering themselves positive to, positive attitude

[Klpno]

Hello everyone,

I'd like to ask about the meaning of "rendering themselves positive to" and "positive attitude" in the following context:

Thought will aid you in the following manner:

2. By the power of direct thought vibrations set in motion by
your mind, which will exert a powerful effect upon the minds
of others, unless they understand the secret of guarding against
these forces and rendering themselves positive to others. An
understanding of this law will also enable you to present a
positive mental attitude toward the thought waves emanating
from the minds of others.

Does "rendering themselves positive to" mean "knowing how to be confident and how to protect themselves from the influence of others"?
And does "positive mental attitude" means "strong mental attitude" here?

Thank you.

[Dozy]

A "positive mental attitude" is a confident, strong and optimistic outlook, which will hopefully help one increase one's levels of achievement and fulfilment, and so forth.

I would expect that if you were "positive to others" you would be quite open and receptive towards them, but the context seems to suggest that almost the exact opposite is meant, which is a bit puzzling. Probably we should not hope for too much coherent sense in a piece about "direct thought vibrations".

[Klpno]

Thank you vwery much, Dozy.