For every impure thought, an unkind word, or sinful action, there must be atonement. There must be something to balance the scale because, without atonement, sin just keeps piling up and up until it crushes you... And in the Old Testament, the blood of animals was offered as a sacrifice for sin. Bulls, goats, rams, and doves were common sacrifices that had to be made daily... Because the blood of animals was only good for so long. The blood of Jesus is eternal, it is holy and makes us whole.