There a couple of things worth mentioning here -
2. Physical / Spiritual If we are talking about messages being received from a god - one that is spiritual in nature and not physical - then we need to tackle the tough question of how the non-material can affect the material. Like it or not, we are physical beings and to implant any thoughts requires some very skilful 'adjustments' to our brain chemicals and our neuron connections. We need to get down to the mechanics of how this might be possible and how we might test to see if it can be detected. Any ideas on this one Dominic?
In answer to 'how does the non material affect the material'. Consciousness = non-material. Sensual perception = material. Consciousness produces perception.
[ I am also equating consciousness = non physical = spiritual = soul, not as dogma or faith but as my definition of 'spiritual' and 'soul' - but the answer to your question is just the paragraph above this one.]