C.S. Lewis’ favourite psalm was Psalm 19. In Reflections on the Psalms, Lewis said of Psalm 19, "I take this to be the greatest poem in the Psalter and one of the greatest lyrics in the world."
In my opinion this three-part psalm perfectly encapsulates Lewis's three-part experience of Joy. Psalm 19 is related to Lewis' description of space in the fifth chapter of Out of the Silent Planet. That passage begins with "He had read of space..." and ends with "the heavens which declared the glory...".
In 1992 I published a full-sized 1993 C. S. Lewis calendar for readers of The Lewis Legacy, and for June I included "The Ten Books That Influenced C.S. Lewis the Most"; this list was composed by Lewis himself in 1962 for a delightful series in The Christian Century.
PHANTASTES by George MacDonald
THE EVERLASTING MAN by G. K. Chesterton
THE AENEID by Virgil
THE TEMPLE by George Herbert
THE PRELUDE by William Wordsworth
THE IDEA OF THE HOLY by Rudolph Otto
THE CONSOLATION OF PHILOSOPHY by Boethius
THE LIFE OF SAMUEL JOHNSON by James Boswell
DESCENT INTO HELL by Charles Williams
THEISM AND HUMANISM by Arthur James Balfour