My memory is LCM's explanation. The Adversary cannot create. He cannot make a spirit for the individual as God does with holy spirit (lower case). So he puts a "wedge" into a person's "door" - which is what seed is. The singing ladies had a song about keeping the door shut tight.
"Out of fellowship" referred to obedience to God - which could mean many, many things. Not just going to fellowship.
LCM was raging against AA, at the start of this thread. Alcoholism is a devil spirit in his world.