If a sacrifice has a permanent blemish, then it cannot be brought “before God,” and therefore everybody agrees that one who sacrifices it outside the Temple is not liable. However, if one sacrifices an animal with a temporarily blemish, then Rabbi Shimon says that he violates a negative commandment and is liable to lashes, but the Sages consider him completely exempt.
The reason of the Sages is clear – a temporarily blemished animal cannot be currently brought “before God,” but what is the reason of Rabbi Shimon? - He bases his opinion on the phrase, “You shall not do everything we do today, each man what is proper in his eyes.” The word “proper” means “proper in the eyes of the man who offers” now, and will become so in the eyes of God later - and it is this action that "you shall not do."
Art: Giovanni Segantini - Il reddito del pastore