In the Old Testament, when God asked for a sacrifice, it was messy business. The slaughter of an animal involved the animal's cries, the gushing of blood, and the smell of death and singed fur. God talks about it as a "pleasing aroma" but I'm guessing it was only pleasing in a spiritual sense. Blood spattered everywhere, and was sometimes purposely sprinkled on the people. It required giving some of your best animals (or grain, as the case may be). For Abraham, it meant raising a knife and preparing to literally slice into the flesh of his son and watch the blood of life drain out of him. It was no mere analogy- he was going to brutally slaughter his son and watch him die.
Later, in the New Testament, sacrifice involved being beaten to a bloody pulp, rejected by your closest friends, and left hanging on a cross to die a slow death.
Thousands of years later, God asks me to make sacrifices, and I act suprised nearly every time that it hurts or gets messy: "Whats this? Blood? Stench? Pain? Woe is me- I didn't see this coming!"
Thankfully, God loves me even when I am dense.