English: “And he shall lean… and slaughter” — just as leaning requires the pure, so does slaughter require the pure. Why is leaning special in that it says “before Hashem”? Slaughter also says “before Hashem”! One could use a long knife and slaughter from outside — hence the juxtaposition teaches purity for slaughter as for semicha.
In the sugya: A long knife might let someone slaughter from outside the required zone while still technically “before Hashem” by reach. Juxtaposition with semicha blocks that loophole: shechitah, like semicha, is tied to a tahor actor in the proper setting.
Type of Learning
Hekesh / juxtaposition of semicha and shechitah — purity required for both.
What Is Learned
Shechitah of kodashim, like semicha, must be performed by one who is tahor. The pairing of the two verbs, and the shared “before Hashem,” is calibrated so that a long-knife workaround does not evade the purity requirement.