There is a special emphasis in the instructions on Old Testament sacrifices - something about the liver and the kidneys. When we think about all of the delicious, fragrant, pleasing parts of a sacrificial animal, these would probably not be our first choice in terms of attractiveness, yet God is quite clear that these are the very parts of the animal that He desires most.
All it takes is a little basic anatomical knowledge, and the answer to this question starts to come together rather easily. What is the function of the liver? What do the kidneys do? Out of all of the organs in the body, it is these two that are most responsible for...filtering blood.
It is the liver and the kidneys that clean waste out of our systems. It is the liver and kidneys that purify, to some degree, the life force rushing through us. It is the liver and kidneys that do the very thing that God is trying to do through the sacrifice itself.
There are, of course, two ways to look at this. The first is to understand that in giving the liver and kidneys to God, we are giving Him these cesspools of filth and sin. It is here where all of our iniquity is stored, having been drawn out of our very blood. It is here where the things that are most toxic to us sit, waiting on the body to do with them whatever the body shall do with them until they become excrement. We are giving to God the raw materials of our own waste, the byproducts of our indulgences, the filthiness of our own hearts.
And we should. God desires that we would trust Him enough, love Him enough, to be vulnerable enough to give Him the most filthy parts of ourselves. He does not relish our brokenness, but He treasures our sacrifice of it. He does not long for our filth, but He handles it with tender care. When we lay our liver and kidneys on the altar, we do so knowing how disgusting and disgraceful these parts of us are, full of scum and slime, and yet, we rejoice, for they are consumed by holy fire and declared an offering, and an aroma, pleasing to the Lord.
The second way we can look at this is perhaps the more obvious: we can understand that in sacrificing the liver and the kidneys, we are offering to God whatever meager ability we thought we had to cleanse ourselves. The blood itself is poured out on the altar; the animal, quartered and divided and roasted. But the liver and kidneys are burned up, for whatever this sacrifice is, it is not so under its own power. It does not cleanse itself.
We cannot cleanse ourselves.
We cannot even cleanse our sacrifices. We can wash them, drain them, cut them, quarter them, roast them, sprinkle them, and a thousand other things, but we cannot run our sacrifices through their own filters. We cannot pull the whole ram, lamb, or goat through its own liver and kidneys. We cannot run all its blood through its organs. We are powerless to offer anything pure, anything clean. The best we can do is acknowledge the feebleness of our sacrifices by making these very thing - the liver and the kidneys - central to our confession. For we are an unclean people.
The Old Testament law can be a bit confusing from time to time. Why does God say this? What does He mean by that? Why would God choose this particular thing over that one? What does it all even mean? But as we talk about the sacrifices and the importance of the liver and the kidneys to a God who seeks nothing more than the cleansing of His people, the wisdom of this particular emphasis is quite clear:
To the One who promises, in all grace and goodness, to cleanse us, we offer these simple tokens - a lobe of the liver, the kidneys, and all of the iniquity built up within that even our best design is powerless, utterly powerless, to cleanse.