OF GODS AND IDOLS:
अचिन्त्यस्याप्रमेयस्य निर्गुणस्य गुणात्मनः । उपासकानां सिद्ध्यर्थं ब्रह्मणो रूपकल्पना ।
God is beyond thought and measure. It does not have any attributes or transformations. Because transformations could be either structural or spatiotemporal. Motion is spatiotemporal transformation. God has no structure, because It is beyond measure. It is omnipresent, hence it has no spatiotemporal transformation, as such transformation implies leaving the position occupied by something and moving to space or time beyond. Such concepts are beyond comprehension by lay men. Hence, for their convenience, the idols have been thought of.
The idol has resemblance to the God or Goddess it purportedly represented. For example, texts by Shilpa Kashyapa and others describe that the Sattwa (light or revealing) aspect of the God or Goddess is expressed through their jewelry. The Raja (mobility) aspect is expressed through their weapons and Tama (covering or inertia) aspect through their vehicles. For example, Lakshmi represents wealth, which is essential for everything and is inherently stationary in nature (we may carry wealth, it does not move by itself). Hence Lakshmi is covered with ornaments and has no weapons. Her vehicle is an owl, because too much money makes one blind to certain aspects of life.
To give one remote example, let us consider electricity. We can achieve wonders by using it, but have we seen it? No. Because it is formless. We only feel its presence through its effects on other bodies. It needs a special wire to flow through it. We can attach a fan to it to get air diffused. We can use an AC for circulating the atmosphere. We can use fridge, heater, etc., for different purposes. Without these gadgets, electricity is of no use to us. Similarly, the Idols are like different Gadgets to get the blessings of God. Muslims pray before Kaaba and different Mazhars. Christians bow before the idols of Christ, the Virgin Mary and the Cross. These are non-Vedic idols.