Taylor Caldwell was a popular author of historical fiction in the mid-20th century. One of her best-known works when I was growing up was “The Captains and the Kings”, the story of an Irish immigrant’s rise to wealth and power in Boston, which was made into a TV miniseries. Most people didn’t have cable TV then, and miniseries were a big deal on TV. People watched them like one would watch Netflix series today.
Taylor Caldwell wrote a number of historical fiction books with Catholic themes, several of which ended up in the “Readers Digest Condensed” book series which many older people of the era when I grew up had in their houses, including my mother, my aunt, etc. I particularly remember “Dear and Glorious Physician” which was a fictionalized life of St. Luke, and “Great Lion of God” which was a fictionalized life of St. Paul (corrected, my memory is going).
The rummage sales were put on by the local Catholic church when I was growing up - so of course there were lots of Catholics cleaning out old books and such and lots of Catholic fiction ended up on the sale tables.
There are actually a ton of really good authors of historical fiction and Catholic-themed or Biblical fiction from about 1900 to 1970s. Mostly forgotten nowadays.
Edited to add, one more interesting fact about Taylor Caldwell: she was not, to my knowledge, Catholic, though she grew up in a Catholic area and wrote very evocatively about Catholic themes.
She was married about 4 times and according to her Wiki biography was interested in reincarnation and new age/ occult stuff. She has been deceased since the 1980s and many of her books are out of print.