To an outsider it would seem odd for someone to bargain for the lives of others, but sacrifice one's son willingly without hesitation. However there are pertinent reasons that Abraham would sacrifice his own son without a second thought. Due to his fear and trust in God, Abraham is able to sacrifice his son without question.
One major reason Abraham sacrifices his only son without question is because he fears God. This is the reason God puts "Abraham to the test". (Genesis 22:1) This test allows God to see if Abraham fears him and therefore listen to his commands. Abraham shows his fear and passes the test by not withholding his "son, your [Abraham's] favored one" (Genesis 22:12). Once Abraham passes the test he is able to receive God's blessing. God knows he will be a fit leader "of a great and populous nation" (Genesis 18:22). Through his fear of God, Abraham is able to sacrifice his son, and eventually secure blessings for himself and his descendants. Coincidentally the same fear of God, which allows Abraham to pass the test, allows Abraham to bargain with God. To fear God is to be humbled by him. Abraham's fear causes him to be humble in his relations with God. Abraham remains humble while he asks God not to "sweep away the innocent" that reside in Sodom and Gomorrah. (Genesis 18:23) Here Abraham displays compassion for his fellow man and at the same time he does not challenge God. Instead he expresses his humbleness by mentioning that he is "but dust and ashes" (Genesis 18:27). Abraham does not dare challenge God, or question that God's decisions are wrong. In fact he shows his fear when he continuously pleads "let not my LORD be angry" (Genesis 18:30). By remaining humble Abraham is able to bargain with God. Even though Sodom and Gomorrah are completely destroyed Abraham is able to save his brother Lot and Lot's children. By demonstrating his humbleness toward God Abraham is able to bargain with God, and that humble attitude is derived from his fear of God.