When there is no enemy within, the enemies outside cannot hurt you. - African Proverb
I've had a tough time with this one, trying to find the deeper meaning here and express it successfully. I think it means that if you are at peace with yourself, if you are not torn or conflicted by things going on in your life, then you will be better prepared to weather the ups and downs of life and less likely to fall victim to the wrath of others. This state of being, however, will not protect you from the physical side of living.