To be spiritual is an attempt to see the world in its intended reality. To see a perspective of this world which the eye alone cannot witness. Instead, the heart itself is used to feel, to see and to hear, and in doing so, to perceive a truth that goes beyond the surface.
To be lacking in the spirit would be to see the world in its reality, but only with the mind of logic and pure rationality, without the sense of "feeling". It reminds me of chasing after desires that have no lasting worth. A habit of those who seek to fill the void in their hearts with the things of this world.
To be over-spiritual... is to see what is in ones imagination, puffing it up, and proposing it as reality. The defining quality of over-spiritualism would be the exaggeration of the mind that seems to supersede the normal intended purpose of things. To make something appear to be more than it is.
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Those lacking in spirit are oft characterised as people who chase after objects of material value that have little worth in the afterlife. The types who seem to place integrity lower on the list. The types who use their bodies for their own devices. It has little to do with religion. Everything to do with principle.
Those who are over-spiritual are oft characterised as the religious who go through extra lengths to credit everything in their lives to something supernatural. They fail to see the world as it is and instead make of it what they imagine to be something much more grand. The danger here lies in the distortion of truth to suit their conceived notions.
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Are we guilty of being either?
Tis not to say that the world is simply mundane. In fact, it is so much in its ordinary state. No need for embellishments. It is beautiful simply because. Something that must be felt, not studied. Stand silent and behold.