Significance of snakes in Vedic literature:

Snakes are revered by Hindus as they are associated with Lord Vishnu and Lord Shiva of the Hindu Trinity. They have been given a place of prominence in Vedic scriptures and thus considered to be powerful and holy. 

The Mahadev (Shiva) is seen with a snake coiled around his neck. The Puranas tell the story of the poison consumed by Lord Shiva, which came out of Ananta, the giant serpent on which Vishnu resides. The poison was held in the neck of Lord Shiva and made it blue. If one drop of it had fallen, the entire Universe would have been obliterated. This can be compared to snakes who also have the capacity to contain things in their neck. 

Lord Vishnu resides on the giant thousand-headed snake called Ananta or Adishesha. The serpent represents the vast Universe, and Vishnu lying on the snakes represents his control over the cosmos. Thus, snakes are associated with the process of creation, sustenance, and evolution.

The term Kundalini is also associated with the imagery of a snake. It is a form of energy located at the base of the spine and is associated with the Goddess Bhairavi. The Upanishads first state the importance of this energy, and it is believed that when one seeks spiritual growth and enlightenment, this energy spikes up across the spine like a coiled cobra that has been awakened.

Snakes symbolize the ever-changing nature of human existence and the will power to adapt to the change. They are sensitive creatures that possess only the sense of hearing and touch. Thus, they are always alert and responsive to the smallest changes. Devotees worship them to gain this wisdom of adapting to change.

Naga Dosha and Sarpa Dosha

Those who injure snakes or kill them are said to be cursed, and this affliction can continue for generations to come. Many people who suffer from failure in their personal or professional life may have had this karma associated with them called Naga Dosha. The affliction may include the inability to produce an heir, skin diseases, low intellect, and poor financial status. 

When all planets are located between planets Rahu and Ketu it is termed Kala Sarpa Dosha. People who are born under the influence of these planets will face difficulties and hence need to perform certain remedial actions. This Dosha is mostly genetic and is passed on from your ancestors who may have injured/killed snakes. The mal effects of Sarpa Dosha are mental unrest, fear and anxiety, chronic ailments, problems in relationships, lack of opportunities in career and financial instability.

Penance for killing snakes:

The best way to ease the ill effects of these Doshas is to perform Rahu Ketu Fire Lab( Homam) and in Anointing/Hydration Rituals ( Abhishekam) to Shiva at his temples. In North India, a special day is dedicated to the worship of snakes called Nag Panchami. It is said that if snakes are worshipped on this day, they will remove the bad karma of past generations and will not harm the devotees.