Our Parsha commands us to be holy, gives examples of what that entails, and then mentions the shelamim (peace) offering (19:2-5). One of the laws of this offering is that it must be consumed before the third day. If any remains, or if there is even intent to have any remaining on the third day, the entire offering would not be accepted. How would the mere consideration of eating it on day three invalidate an offering if it didn’t end up happening anyway?
Rabbi David Fohrman suggests that the answer can be derived from the topic mentioned thereafter. After these offering details, the Torah speaks of social justice rules, such as the leaving of one’s harvest for those less fortunate, honoring one’s commitments, and not stealing. All these ordinances aim to build respect for others. This same respect for others would prevent one from even considering breaking the shelamim 3-day rule. Respecting and honoring the boundaries of G-d and of people will enable us to lead holy and just lives.