Other than the sometimes-fussy YHVH, there's only one other deity in town in Leviticus: Molek. And boy is this guy a royal pain in God's holy backside.
No matter how many times God tells the Israelites not worship this Molek guy, they never seem to listen. Whether Molek actually exists doesn't really matter. What matters is that the Israelites are worshipping him.
The problem? People see Molek as one of God's crew, and worship includes passing children through fire as a sacrifice. But when God gives Israel children, dedicating them to another deity is a rejection of the covenant. Abundance comes from God, and he is shocked—shocked that Israel would think he wants people to sacrifice their kids. Death penalty, here we come.
P.S. The association of Molek with a dastardly God is such a powerful image that it continues to show up in literature and film today. Remember Allen Ginsburg's Howl turns Molek (there called Moloch) into the god of American industrial capitalism. Yowza.
Pretenders to the Throne
The Bible wouldn't be the Bible without some punny subtext. And Molek is no exception. The Hebrew root m-l-k means king, and some commentators think that the Israelites may be confusing Molek the king with God, their spiritual king. So hating on Molek might be a warning against trying to set up a new Israelite kingship or a coded message not to give the rising generation over to Persian control. Either way, pretty sneaky.