This means that the spirit of the individual is unable to perceive. It is unable to function as it should. It is walled off and sleeping. It is unable to receive any messages from spiritual heights and consequently it is isolated and abandoned to whatever danger threatens it.
The individual here has lost all insight. This is often the result of excessive intellectual activity whereby the individual relies only on the intellect for all his decisions. He has thereby over many an incarnation neglected to use his spirit for his decisions. As a consequence, this spirit became accustomed to not being used and as such lies sleeping and immured within him.
Another reason for this condition is indolence. The individual fails to rouse his spirit to activity and also relies on the intellect for all his decision-making. People with this condition are unable to understand spiritual matters when these are being discussed and are also unable to receive any messages from the spiritual realm. They will also not be able to recognize spiritual messages or teachings or those who bring these messages.
This was the case during the life of Jesus, the Son of God, whereby those who were supposed to be the representatives of God on earth were the very ones who opposed Him. They could not recognize Him because they were spiritually blind and as such could not see Him. They did not recognize His Message because all the sense organs for use in this regard were dead.
To be spiritual blind is therefore a serious matter and the consequences can be spiritually fatal for the individual. Such a one who is spiritually blind can never attain to salvation for his spirit because he will never recognize the teaching that brings this salvation or the one who brings salvation in the Word.