All Things and Beings are Worshipful
In Indian homes, we are taught from a very young age, never to touch papers, books and people with our feet. If the feet accidentally touch papers, books, musical instruments or any other educational equipment, children are told to reverentially touch what was stamped with their hands and then touch their eyes as a mark of apology.
Instruments of Knowledge
To Indians, knowledge is sacred and divine. So it must be given respect at all times. Nowadays we separate subjects as sacred and secular. But in ancient India every subject- academic or spiritual- was considered divine and taught by the guru in the gurukula.
The custom of not stepping on educational tools is a frequent reminder of the high position accorded to knowledge in Indian culture. From an early age, this wisdom fosters in us a deep reverence for books and education. This is also the reason why we worship books, vehicles and instruments once a year on Saraswati Puja or Ayudha Pooja day, dedicated to the Goddess of Learning. In fact, each day before starting our studies, we pray:
Saraswathi namasthubhyam Varade kaama roopini,
Vidyaarambham karishyaami Sidhirbhavatu me sadaa
(O Goddess Saraswati, the giver of boons and fulfiller of wishes, I prostrate to You before starting my studies. May You always fulfill me.)
The Divinity in All Beings
Children are also strongly discouraged from touching people with their feet. Even if this happens accidentally, we touch the person and bring the fingers to our eyes as a mark of apology. Even when elders touch a younger person inadvertently with their feet, they immediately apologize. Read about why do we prostrate before parents & elders?
Man is regarded as the most beautiful, living, breathing temple of the Lord! Therefore touching another with the feet is akin to disrespecting the divinity within him or her. This calls for an immediate apology, which is offered with reverence and humility.
Thus, many of our customs are designed to be simple but powerful reminders or pointers of profound philosophical truths. This is one of the factors that has kept Indian culture alive across centuries.
Reference: Why do we… by Swamini Vimalananda and Radhika Krishnakumar