Idol Theory

According to Index, the Idol Theory is a form of basic knowledge that allows magicians to put the power of God and angels to good use.

Theory
Following this theory, if one were to build a duplicate of the cross when Christ was crucified, and put it on the roof of a church, they’ll get some Holy power from those actual Cross wielders. Although the power of the duplicate is not even 0.000000000001% of the original, and even the legendary strongest duplicate Holy Manger has only a small fraction of the power, if they were to get even 1% of the power of the original, their power could match even those of the twelve apostles. Kamijou Touma compares this to the Sun providing solar power for electricity as the power of the 'original' is almost limitless even with the power split across so many duplicates. One hypotheses related to this theory is that it can be switched around. In other words, not only will the original cause some effect on the ‘Idol’, the ‘Idol’ can also affect the original. This is a considered a hypotheses as their are some exceptions which cannot be explained. This hypothesis is used by people claiming that they’ll receive divine judgment if they treat the Bible badly. Index claims this isn't unreasonable as there are many instances in the Bible where several ‘Idols’ from different Greek religions that are against Christians are struck down and destroyed by lightning. The theory cannot be used, however, once the original 'image' is changed. As long as there’s a slight difference in the level of magic used between the idol and the original, the idol will lose it’s purpose.

Usage
In Japan, the famous mapmaker Ino Tadakata used the Idol Theory in a reverse matter. Using it he plotted 47 ‘portals’ on Dai Nihon Enkai Yochi Zenzu, an intricate map of Japan created by Ino Tadakata, that originally didn’t exist on the Japanese islands. This caused these entrances that allow people to come and go as they please appear in modern Japan. In the entire history of magic, he is the only person who has been able to add something to the duplicate that the original didn't have while maintaining a perfect balance between the duplicate and the original.