The Almighty God appointed Abraham to guide the deceived people and idolaters. So he was honored to be granted the high position of prophet hood. Abraham had a faithful heart, he had no doubt about his God's power but he wanted the reality of things to become clear to him and thus invest his insight. So he sincerely asked his God to show him how his Greatness could revive the dead and bestow life upon them.
He was so addressed by God:"Haven't you believed resurrection yet?"
Abraham said:"I do have faith but I am eager to see the reality of things to make my certainty and faith just firm."
Since Abraham had no intention rather than being reassured, the Almighty God sent him a revelation:
"Catch four birds and after killing, mash them all together into a pile then, divide the pile to different parts and put each part on the peak of a mountain, call them one by one and you shall see that they all revive with our permission and shall come to you"
He did so and when he called them, the pieces gathered from the piles and joined together to make four birds once again alive through God's will. Abraham observed one of the greatest manifestations of God's power in making the dead a live. His heart which was full of faith was now so highly reassured.