As a Catholic, I have understood this in a general sense, but not in the particular one in regard to my own family.
This insight came to me a couple of months ago when I attended a Catholic prayer weekend about healing your family tree.
We were told to write down all the names of our departed relatives for whom we wished to pray, and then these pieces of paper were placed in a basket beneath the altar before Mass.
When the consecration of the bread and wine into the body and blood of Christ took place, I was suddenly overcome by deep, gut-wrenching grief.
I began crying unconsolably without knowing why.
Then I was given to understand that most of the souls I was praying for had never had anyone to pray for them.
Once they had died, they had been forgotten.
One of the people I prayed for, a woman, was from the early convict era of the penal colony of New South Wales.
I was so moved by what happened - it was as if the lights had suddenly been turned on in my heart and head - that I have vowed to keep praying for my ancestors.
I have written all their names down in a small leather-covered notebook with a cross and the words 'Pray for Souls' written on the front.
At each Mass I attend I open it at a particular page and, at the consecration, pray for the names written there.
When I did that this morning, I was close to tears again.
Very few of my Mawbey ancestors were Catholics as far as I am aware.
They were mainly of the Church of England or Wesleyan Methodists.
My father's mother, Mary Edwards, was a Catholic and so were all the children she had with John Mawbey (2), the eldest son of Sarah Mawbey, murdered by Jimmy Governor.