Our Gemara on Amud Beis described the process of slaughtering the olah bird offering. One difference between the olah bird offering and the chattas bird offering is that the head of the olah is fully severed, while the chattas bird’s head is not fully separated.

Shem Mishmuel (Vayikra 6) offers a compelling psychological explanation for this difference between the chattas bird and the olah. We have a tradition that the function of the olah is to atone for improper thoughts. Shem Mishmuel asks rhetorically: how can we be held responsible for our thoughts that are numerous like the “raging sea which can never be quieted”? God does not make tyrannical demands. Therefore he asserts that we are not responsible for the thoughts as they come up. However, if we let them enter our hearts, then we are responsible — meaning if they move from intellectual contemplation to a visceral emotional state. The way I understand this is: a person can think about something that makes him angry, but feeling emotionally angry is the next step. Or a person can intellectually note, “oh that is an attractive woman,” but entering into a state of lust is the emotional next step of allowing it into the heart.

The olah sacrifice involves completely separating the head to symbolically achieve the proper boundary between the head and heart. The person cannot control seemingly random thoughts that pop into his head, but he must not dwell on them and enter into an emotional state, i.e., allowing them into the heart.

(This is similar to a ruling by Ezer Mikodesh, EH 23:3, who says one only violates the prohibition against forbidden thoughts if he deliberately dwells on them, not if they merely flit by his thoughts.)

The chattas, on the other hand, is most typically brought for sins committed out of negligent lack of awareness. In this respect, the opposite is true: the head is NOT connected enough to the heart and the person is acting without thinking enough. Therefore, the chattas bird’s head is NOT fully severed so as to symbolize and correct the disconnection between the head and the heart.