To study, memory is important. To memorise, every student is advised by his teacher to make mind-maps and diagrams, write notes and use minimum keywords. Thus, diagrams, flowcharts and such presentations with colours, pictures and abbreviations help create a mind map to memorize knowledge. Unless knowledge is stored in memory, it cannot be tapped and applied when needed. Companies create logos to convey their business. Management uses several models to structure thought process, and motion graphics to explain concepts. Imagine, if you do not have pen and paper, books and computers, then what tools you would use to build graphic image to structure knowledge in the mind? Idols and symbols was the answer. They hide knowledge which needs to be deciphered, as its meaning is lost. In Sruti periods, icons and idols became a great help in preserving knowledge with the support of personified mythologies.  To capture the concepts, virtues and knowledge, icons, idols and mythologies were tactfully used. Symbols of Gods, AUM, Swastik etc. have great meaning as explained in section of symbolism. Refer to the section on symbolism to understand their meaning.
Indians due to Bhaktiyog cult remained the most humane community in the entire world and never invaded any other country, after Mahabharat. Although there were religious preferences and acrimony, but it never converted into bloody wars, with mass destruction and plunder. India absorbed all the foreign invasions bravely, but never lost its original culture and religion, at least in practices. Although it did lose the attitude of original thinking and creation of knowledge, as a community. As individual people still possess such attitude, which remains untapped and unpromoted. Ancient Indian culture and knowledge spread to almost all of South East Asia and even to Middle East and pre-Christian Europe. The cultural fossils of which can still be found in similarities in the names, rituals, festivals, traditions and myths. The biggest reason why Sanatan Dharma could survive for thousands of years is due to inherent flexibility it offers including monotheism, polytheism and atheism in its four-fold Yoga philosophies, which offered mutual tolerance and respect to each other, in the name of God, thus very little internal wars.
Incidentally, the knowledge of Ayurveda froze. Knowledge of weaponry froze for a long time. Knowledge of aviation got lost and Pushpak Vimaan became a mythological narration. Knowledge of humanity or Sanatan Dharma also froze. We are made to feel proud using a foreign word ‘Hindu’ for our religion, rather than using Sanatan Dharma, as original and characteristic name. The fundamental knowledge of religion and humanity is being subsided by the rituals and symbolic worships. This may be said to be the negative impact of idolism. Yet it does not overweigh the positive role it plays in preserving religion. The error is in interpreting it correctly. Time has come to revisit our symbols and icons and decipher it properly, thereby contribute the growth of humanity on the planet, with knowledge, which has always been the strength of Sanatan Dharmis.