A few days ago I was in Jogjakarta, Indonesia to witness the Idul Adha ceremonies at the most influential Javanese sultan's palace.  It starts with morning prayers toward Mecca, men & boys in front, women & girls in the back.

Later, everyone gathers in their neighborhood to slaughter the sacrifices of Id. 

 Neighborhood boys and babies in their father's arms witness the slaughtering of the goats, sheep & cattle--an important part of their socialization.

It's a memorial to Ibrahim, who loved & trusted Allah so much that he was willing, on Allah's command, to sacrifice his beloved son.  At the last moment, Allah provided an animal as a substitute to die in the place of his beloved son.  Once a year Muslims commemorate Ibrahim's faith & obedience by coming together, sacrificing animals, & then giving the meat to the poor.  

In many parts of the Islamic world this is the most important holiday of the year.