Answer:
Everything in this earth, in fact in this universe exist in the form of energy and in different realm of existence. We have the seen and the unseen realms, the form and formless realms. We are unable to contact each other of different realm as we are of different frequency, like a radio or a TV can tune into different channels by changing the frequency. Spiritual beings are higherly evolved and are always looking forward to help the less evolved, just like we humans looks forward to help the less fortunate fellow beings or the less evolved being like animals and plants. Since the spiritual beings are unable to contact 'directly' to help others beings, they need a channel, they need to tune in to different frequency in order to help. If you are a gifted or highly evolved human you can be that 'conduit' to tune in the frequency of the spiritual being and link to the more unfortunate human that needs the spiritual guidance from the spiritual being. To paraphase, in order to be a spiritual guide you are gifted (divine calling) or trained yourselve to be highly spiritual to create the correct energy during the conduit of energy.