Lewis was eighteen when he first read Arcadia, the year before he entered Oxford and also the Army, refusing his Irish exemption. Connection?
192-3 (to Arthur Greeves, 14 June 1916): Lewis is “strongly tempted” to buy Arcadia in CUP ed. “One thing that interests me is that Sidney wrote it for his sister, the Countess of Pembroke, sending it to her chapter by chapter as he wrote it as I send you ‘Bleheris’. Perhaps we were those two in a former state of existence—and that is why your handwriting is so like a girl’s. Though even my self conceit will hardly go as far as to compared myself to Sidney” (193).
196-7 (to Greeves, 20 June 1916, from Kirkpatrick’s): The Arcadia “is a glorious feast: I don’t know how to explain its particular charm, because it is not at all like anything I ever read before: and yet in places like all of them. Sometimes it is like Malory, often like Spenser, and yet different from either. For one thing, there is a fine description of scenery in it (only one so far, but I hope for more) which neither of them could have done. Then again the figure of the shepherd boy, ‘piping as though he would never be old’ rather reminds me of the ‘Crock of Gold.’ But all this comes to is that Sidney is not like anyone else, but is just himself. The story is much more connected than Malory: there is a great deal of love-making, and just enough ‘brasting and fighting’ to give a sort of impression of all the old doings of chivalry in the background without becoming tedious: there is a definite set of characters all the time instead of a huge drifting mass, and some of them really alive. Comic relief is supplied by the fussy old king of Arcadia—rather like Mr. Woodhouse in Emma—and his boor, Dametas. The only real fault is that all the people talk too much and with a tendency to rhetoric, and the author insists on making bad puns from time to time, such as “Alas, that that word last should so long last.’ But these are only small things: true, there is a good deal of poetry scattered through it which is all detestable, but then that has nothing to do with the story and can be skipped. I’m afraid this description won’t help much, but I am just longing for Saturday when I can plunge into it again. (I mean the book, not the description).”
199 (to his father, 23 June 1916): “I am at present enjoying a new liteary find in the shape of Sir Phlip Sidney’s ‘Arcadia,’ which I got at a venture and found better than I expected: though like De Quincy’s and Southey’s epics, ‘I expect that I enjoy the priviledge of being the sole reader of this work.’”
201-2 (To Greeves, 28 June 2016): “In the meantime the ‘Arcadia’ continues beautiful: in fact it gets better and better. There has been one part that Charlotte Bronte could not have bettered: where Philoclea, the heroine, or rather one of the heroines, is beginning to fall in love unconsciously with a man disguised as a girl: and she does not know the secret: the delicacy and pathos of her wrestlings with a feeling which of course she can’t understand, as told by Sidney are—well I can’t explain what they are like: there is one scene where she goes out by moonlight to an old grove, an haunted place, where there is an altar to ‘the wood gods of old,’ and lies looking up at the stars and puzzling things, that is equal to if not better than the scene where Jane Eyre wakes up on the moor—do you remember? On the other hand, of course there are parts YOU might not have patience with: in the old style, where people relate their own adventures with no direct bearing on the main story: yet even this, to me, is interesting—so quaint and so suggestive of the old romantic world.”
205 (to Greeves, 4 July 1916, when Lewis is refusing to take an Irish exemption from the War, disappointing his father): “So you feel hurt that I should think you worth talking to only about books, music, etc.: in other words that I leave to others all the sordid and uninteresting worries about so-called practical life, and share with you those joys and experiences which make that life desirable: that—but now I am getting rhetorical. It must be the influence of dear Sidney and his euphuism I suppose.”
207 (cont.): “I am still at the ‘Arcadia’, whichyou will gather from this is a long book, though not a bit too long. I won’t make you sick of it before you see it by starting to sing its praises again: I only promise you that I am still as keen on it as when I began.”
209 (to his father, 7 July): “I for my part am still at my ‘Arcadia’ which I find excellent.”
211 (to Greeves, 11 July): “That feast the ‘Arcadia’ is nearly ended: in some ways the last book is the best (though a little spoiled I admit by brasting) and here the story is so like the part of Ivanhoe where they are all in Front-de-Boef’s castle, so that I think Scott must have borrowed it.”
214 (to Greeves,  July 2016): “The ‘Arcadia’ is finished: or rather I have read all there is of it, for unfortunately it breaks off at a most exciting passage in the middle of a sentence. I will not praise it again, beyond saying that this last 3rd book, though it has no such fine love passages as the 2nd, yet (despite the brasting), for really tip-top narrative working the interest up and up as it goes along, is quite worthy of Scott.”
Lewis was reading the first volume of Feuillerat’s edition, published in 1912, based on the 1590, with chapter divisions.
547 (to E. R. Eddison 19 Jan 1943, imitating an archaic style): “Is Sir Philip Sidney’s incomparable Arcadia among your books? If it bee not, I conjure you to rede it (not heeding all the fine criticks) for I beleue it was written for you.”
562: (12 March 1943): “My own favorite reading, though it does not overlap yours except at Amadis, is somewhat akin—the Morte Darthur, the Orlando Furioso, the Faerie Queene, the Arcadia, the High History of the Holy Grail & all Wm Morris, but especially his prose romances.”
563: (same): “An early & lasting love of Oriana, Bradamante, Philoclea & the rest at least preserves us from Fiorinda [lady of honor in Mistress of Mistresses], about whom I think as you do (I told my friend that I had no use for his ‘metaphysical mistresses, hyper-uranian whores, beautifical bona-robas, and transcendental trulls’). [The friend is Eddison, author of The Worm Ouroboros, where Sophonisba appears.]
644 (22 April 1945, to someone coming back to college from the Navy): “Now is the time for Chaucer, Malory, Spenser, Sidney, Shakespeare, Dryden, Pope, Swift, Johnson, Fielding, Richardson, Cowper, Scott, Wordsworth, Byron, Dickens etc. etc. . . . I myself always index a good book when I read it for the first time noting (1) Linguistic phenomena. (b) Good & bad passages. (c) Customs: meals times, social classes, what they read etc. (d) Moral ideas.” (2:644)
683 (12 December 1955): “The tide may yet turn, but I never thought that a good support: ‘Hope is the fawning traitor of the heart.’” [Hooper corrects it to “of the mind,” Arcadia 3.27, said by Pamela, resolved to die to keep her honor.]