After Adam had fallen, Lucifer took him in, made him sign a contract and become his property,aka sell his soul to him.

Lucifer was currently frustrated, trying to get Adam to eat something today, anything. But each time he did, he'd get his hand slapped away.

"Adam, please, eat it.." Lucifer was begging at this point, tugging at the golden chain around Adam's neck just a bit, not wanting to hurt him.