The Mishnah, at the beginning of Zevachim, states: לִשְׁמָן שׁ ֶלֹּא שׁ ֶ נִזְבְּ חוּ ה ַזְּבָח ִים כָּל הַחַט ָּאת וּמִן הַפֶּסַח מִן חוּץ ...כְּש ֵׁרִים. The intention is as follows: Ideally, all korbanos should be brought l'shmah. This means that when a kohen brings a korban olah, he should think that it is a korban olah when he sacrifices it and makes the korban. If the korban is a korban shelamim, he should think that it is a shlamim as he sacrifices and makes the korban. However, even if the kohen made a mistake, and he thought it was another korban, the korban is kosher, b'dieved. For example, he thought the olah was a shelamim, or he thought the shelamim was an olah – the korban is nonetheless kosher. It wasn't brought l'shmah, in the best way, but the korban is nevertheless kosher. However, the Mishnah tells us, there are two exceptions: they are the korbanos of chatas and korban Pesach. These korbanos must be brought l'shmah, and if they weren't brought l'shmah, the korban is pasul. If one brings a korban Pesach or a chatas, while mistakenly thinking that it is a korban olah (or some other korban), the korban is pasul.
Why are these two korbanos (chatas and Pesach) different than all the other korbanos? Why do they become pasul when they are brought shelo l'shmah?
Imrei Emes zt'l answers that these korbanos represent new beginnings. The korban Pesach is among the first mitzvos that Bnei Yisrael were obligated to perform, and a korban chatas is when a person is turning over a new leaf and is beginning to improve his ways and do teshuvah. A first mitzvah must be done l'chatchilah, in the most perfect manner. Then, all mitzvos that come after it will receive the impact from the first mitzvah, which was performed with perfection. Therefore, these two korbanos can't be brought לשמה שלא.
The Ropshitzer zt'l said that Avraham succeeded in his avodas Hashem because he didn't think about the past. If he had thought about the beginning of his life, the days he worshipped avodah zarah, or if he would think about his origins, his yichus, his parents who gave birth to him, he would have lost hope in serving Hashem. Hashem told Avraham לך לך, go forward. Don't focus on the past. Only in this manner will you be able to succeed in avodas Hashem.
This is a lesson for all Yidden, because we must go in the ways of the holy Avos. לך לך, forget about what was, and begin anew, now.
