LEV1153 If an animal sacrificed for the Altar is switched for another, both animals are sanctified. Hashem wants to instill fear into our hearts regarding all matters of holiness. Accordingly, He commands in His Torah that once an animal is sanctified for the Altar, its holy status becomes fixed forever and one cannot tamper with it. One should not think that he has the power to remove the sanctity and dedicate a different animal instead. If a person transgresses this command and says, “This animal shall be in the place of that one,” his plan backfires and both animals are holy. Since the person tried to annul an animal’s sanctity he winds up causing its sanctity to spread onto another animal. Property that someone dedicates to the Beis HaMikdash but not to the Altar can be redeemed. The item’s monetary value plus one-fifth is given as redemption money; thereby the holiness is that attached to the item when it was dedicated transfers onto the redemption money and the item leaves the possession of the Beis HaMikdash. According to the Rambam, the Torah here reads man's mind and copes with a human foible. Man by nature enjoys accumulating possessions. He becomes very attached to them and does not want to part with them, so if he dedicates some of his property to the Beit HaMikdash, he might regret what he did. He might want to redeem the item so he can have it back, but will not want to pay its full value. For this reason, when one wants to redeem his dedicated object, the Torah requires him to pay the value of the principal plus one-fifth. Similarly, regarding animals dedicated to the Altar, were the Torah to allow us to exchange one animal and dedicate a better one in its place, people would come to switch dedicated animals for worse ones, too. Therefore, the Torah closes the door on the entire possibility.