Servant of God Ibrahim vowed that if God gave him a child,he would sacrifice the child in appreciation to him Allah.
Allah fulfilled his promise by giving Ibrahim a son who was named Ishmael but when the time came for Ibrahim to fulfil his promise,he became reluctant.
Allah reminded him in a dream but he still draged his feet until Angel Jibril reminded him that as a prophet,he should take dreams from Allah seriously.
Next was how to convince his son Ishmael on his vow to sacrifice him to Allah but his son agreed willingly to be offered as a sacrifice.
Despite the difficulty in fulfilling his promise to slaughter his son but was on the verge of doing it,Allah provided a ram which was slaughtered in replacement for his son.
That basically is the story behind the festivities being the obedience to God by Prophet Ibrahim and the Submission by Ishmael to Allah to be slaughtered.
That is a big lesson of IBADA(faith) to our Muslim Brothers.