Of all the Yajna Annadanam is considered one of the most important. Annad bhavanti bhutani (All living beings subsist on food grains).This sloka from Gita tells us how Annam is closely knit with all living beings.
The above sloka from Bhavishya Purana tells us to give annam as danam.Without Annam one cannot imagine the existence of nature itself.
"അന്നമേവ മനുഷ്യാണാം പ്രാണാനാഹുര് മനീഷിണ: "
Annam is the life force(pranan) and life force is annam as told by great saints.
Ramayanam also speaks about Annadanam done by King Dasaratha and Lord Sree Ram.Of all the Yajna conducted Annadanam is considered to be the most important one.
"കാലെ വര്ഷതി പര്ജന്യ
സുഭിക്ഷം വിമലാ ദിശ:.."
Annandanam should be conducted in abundance as told by Kula Guru Vashishta muni.Always maintain equal respect for all the people who take part in Annadanam and do not differentiate people based on character,status etc.Annam should be distributed equally to all.All sections of people should be invited and everybody should be equally respected.This shows our ancient Bharath varsh culture.
നിമന്ത്രയസ്വ നൃപതീന് പൃഥിവ്യാം യേ ച ധാര്മികാ:
ബ്രാഹ്മണാന്, ക്ഷത്രിയാന്, വൈശ്യാന്, ശുദ്രാന്ശൈ്ചവ സഹസ്രശ:
While doing Annadanam there should not be any differentiation based on caste,creed or color.Everybody should be treated equally ..This rule holds good while inviting people for Annadanam.Also there should not be any distinction observed for people invited and not invited.Just by doing Annadanam a person will not get elevated to a higher spiritual level unless it is done with total dedication.
Swamiji narrates an incident about Brahma Sree Neelakanta Gurupadar.Gurupader after performing Pattabhishekam gives the Nivedyam to the dog who is waiting for the prasadam by his hand instead of throwing it near the dog.Also eats the leftover from his hand.The above act of Gurupadar shows the level of sanctity maintained for all living beings while doing Annadanam. .
The above points are taken from Padapooja book written by Jagadguru Swami Sathyananda Saraswathi Tiruvadikal .This book is an exhaustive text on the Guru -Shishya relation between BrahmaSree Neelakanta Gurupadar and Swamiji and the significance of the interactions of the Guru with the disciples and devotees.