I doubt if the song has metaphoric meaning. It's about being poor and being hungry.

In 1983 I had a co-worker who was 15 years older than me. Her husband was that much older than her. She talked of how poor he was growing up, and how his basic food was beans and cornbread.

If some smarmy deacon comes around and manipulates Mama into giving him their lard, how will she make the cornbread? The deeper meaning here isn't sexual, it's anti-clerical.

Plus, if they are lucky, once in a while they'll have fried chicken, and they need the lard to fry it.

There actually are people in Missouri to this very day who fry their chicken in lard. I name no names.