I can't provide references, but an observation: humans exist at various levels, that is, physical, astral, and causal. So, in a sense, do idols. In themselves, they are pieces of metal or stone, and we don't worship physical substances, we direct our prayers and devotion to the being represented by the idol. But at the same time, as we relate to an idol and continue prayer and acts of devotion and puja, it becomes "energized" and is then a mode of presence of the deity in the temple or in our homes. It is a link between the divine and human realms, just as our own bodies and minds are the same. Anyway, that's my opinion, and hope it helps a little.
Peace, Shakti