“...Secular writers like Alexander Solzhenitsyn...”
Solzhenitsyn was not a secular writer. His writings are Christian although his Christian themes are sometimes approached subtly.
“Solzhenitsyn was not a secular writer.”
He was not a priest or monk or bishop. Hence, his writings, although overtly religious, could be considered secular because they were written in the world and not behind the walls of a monastery. That is the traditional use of the term “secular”.