Why is Holi celebrated

In the ancient time there was a demon named Hiranyakashyap he after too much penance he got a boon from Lord Brahma that any organisms, Gods or Godess can never ever defeat or kill him or even he said that no one can kill him in morning, in afternoon or in night then or not in house in outside or no ethology can defeat him then Lord Brahma give him his boon.

Then after this he did too much unrighteousness on planet earth then he got a son named Prahlad who is on the path of righteousness and never ever done a bad thing and he was a devotee of Lord Vishnu. And after some years when he was young Hiranyakashyap said to him that you cannot praise anyone rather than me then Prahlad was too upset and as he was a devotee of Lord Vishnu he refused to do that then Hiranyakashyap was angry and he planned many plans to kill him.

But he wasn't successful at that as Lord Vishnu was doing courtesy on him. And then one day Hiranyakashyap remembered his sister named Holika. And she had boon blanket that can never burnt in fire. And then one day Hiranyakashyap called her sister Holika to kill Prahlad and then Holika came with her blanket and she put Prahlad in her arms and sat on the fire and then Lord Vishnu show his courtesy to his devotee Prahlad then the blanket was fell on Prahlad and then after this Holika doesn't have blanket and then And it is also known as festival of colours and the day before Holi is celebrated as Holika dehan and also known as chhoti Holi and this day all the people worship on Holika and then after a day it is burnt at night time.

Let's back to the story then Prahlad was safe and to kill Hiranyakashyap Lord Vishnu incarnate into Lord Narsinh and Lord Narsinh was a man who have claws and face of a lion and left body parts were of a human being. So there is no organism like that so that boon is not broken and it is not breakable and he put him on the line entrance of house so that's why the boon is also completed in the eye of righteousness.