The Queen has said she is "very grateful" for the country's prayers and that she has felt God's "faithfulness" throughout her reign.
Writing in a foreword for a new book, The Servant Queen And The King She Serves, the monarch writes of her enduring Christian faith.
The book, published by the Bible Society, churches' group HOPE and LICC (the London Institute for Contemporary Christianity), is being released in April to mark the Queen's 90th birthday.
She writes: "I have been – and remain – very grateful to you for your prayers and to God for his steadfast love. I have indeed seen his faithfulness."
In her comments, the Queen refers to the changes she has seen in her life, which has made her the longest-reigning monarch in British history.
"The extent and pace of change has been truly remarkable," she said.
"We have witnessed triumphs and tragedies."
The monarch also took the opportunity to allude to the current problems in the Middle East saying the world is now experiencing "terrible suffering on an unprecedented scale".