Rashi on Leviticus 19:5/רש"י על ויקרא י״ט:ה׳

1'וכי תזבחו וגו‎‎ AND IF YE SACRIFICE [A SACRIFICE OF PEACE OFFERINGS UNTO THE LORD, YE SHALL SACRIFICE IT TO BE ACCEPTABLE TO YOU] — This section is said only for the purpose of teaching us that their (the peace offerings’) slaughtering must not take place except with the intention that they should be eaten within this time (the time prescribed v. 6); for if its purpose were to fix the time for eating them it would be redundant, since it is already said (Leviticus 7:16) “But if the sacrifice of his offering be a vow, or a free-will offering [it shall be eaten the same day… and on the morrow” (Sifra, Kedoshim, Chapter 1 1).

2לרצנכם תזבחהו YE SHALL SACRIFICE IT TO BE ACCEPTABLE FOR YOU — This means, from the very beginning the slaughtering shall be done with the intention to give Me satisfaction (i. e. to sacrifice it in a manner that is satisfactory to Me) so that it shall effect favour for you (לרצנכם). For if you have in connection with it (with the slaughtering) any intention which will invalidate it (the sacrifice) it shall effect no favour for you before Me.

3לרצנכם thus means as much as apaisement in O. F., — “favourable acceptance”. This is the literal meaning of the verse. Our Rabbis, however, (taking the word in its primary sense of will, “intention”) learned from here as regards one who is handling (מתעסק) a sacrifice (קדשים) (when he does the act of Shechitah without the intention of doing this) that it becomes invalid, because it is required that he should intend to slaughter it (Zevachim 47a; Chullin 13a).