The idol is in the dark Garba griha and maintained in similar temperature to the womb. It symbolizes the God/Goddess within us. It has got the few lamps lit and that adds to the warm temperature. The idol symbolizing the God / Goddess is also dark - cannot be easily viewed. This teaches us that God cannot be seen easily. He has to be searched with dedication and alertness in seeking within us.
Secondly even with the lamps he is not easily visible. The priest performs different abhishekams and tries to show the God in different forms using the Deepam Araadhanai after each. This teaches us that we see the God in the form that we decorate him/her. We see the truth in the way we decorate the truth. Like viewing with tinted glasses, we see every information with our own prejudice and decorations. Hence we need to understand that to really see the truth or God within we have to remove our own prejudices and decorations.
Thirdly the bell that is rung either at entrance of some temples (devotees can ring it) or during Deepam Araadhanai, is to wake up the God within us. It is not to call out to God & ask for money, status, promotions, etc.
Fourthly we tap our cheeks also to improve our alertness and wake up to the truth that is tried to be displayed within the Garba Griha by the priest using the deepam aradhanai.
Hence, every action is to help us seek and wake up the God within us. It helps us understand what is truth, how we look at truth and how we should look for truth in everything around us. It is not a place for negotiating deals with the God as some seem to do at temples.