God could read what was lurking in the heart of Cain & gave him warning----And the LORD said unto Cain, Why art thou wroth? and why is thy countenance fallen? If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. / It desires to have you, but you must rule over it.”
Genesis 4:6,7 KJV/NIV
Sin lies at the door. It is crouching waiting to pounce if we give it the chance.