The importance and need for Tarot (or some other kind of Divinational tool) is based upon the following facts/beliefs:

The belief/fact that one is ultimately not fully aware of one’s needs, desires, flaws, imbalances and lacks. It is impossible for someone to be fully aware of the totality of him or herself, as one can not be aware of all life.
The belief/fact that there is a omnipresent, omnipotent and omniscentient energy, power, and/or force field of awareness, consciousness, and/or intelligence that exists within, without, above, below and beyond, connecting us all throughout time and space.
The belief/fact that this intelligence is, just like we are, conscious and that there can thus be an exchange of intelligence, data, understanding, knowledge and/or information.
The belief/fact that what is described in 2. is loving and benevolent and can guide us towards what we absolutely, ultimately and/or truly want, need, lack, seek or need to know, see or understand.