"He is no fool who gives what he cannot keep to gain that which he cannot lose."

     Jim Elliot, of course, as cited in some detail by the Archives of the Billy Graham Center at Elliot's alma mater, Wheaton College.
     But according to the Archives, as corrected by reference to the original, which has "that which" instead of "what", also Philip Henry (1631-1696):  "He is no Fool who parts with that which he cannot keep, when he is sure to be recompensed with that which he cannot lose." 
     Thus,

• 1949 October 28, and later in publication:  Jim Elliot:  "He is no fool who gives what he cannot keep to gain that which he cannot lose."
• 17th cent.:  Philip Henry, as quoted by his son Matthew Henry in 1698 (a 1712 printing of this being the earliest I've found online so far):  "He is no Fool who parts with that which he cannot keep, when he is sure to be recompensed with that which he cannot lose."

     I have not gone looking for anything earlier.

"The great achievement is to lose one's reason for no reason. . . ."

"'a knight errant deserves neither glory nor thanks if he goes mad for a reason.  The great achievement is to lose one's reason for no reason, and to let my lady know that if I can do this without cause, what should I not do if there were cause?'"

Sancho Panza, in Miguel de Cervantes, Don Quixote I.xxv (trans. Edith Grossman (New York: HarperCollins Publishers, Inc., 2003), 194).

"the inference that makes science": the abduction/retroduction inclusive of deduction, induction, and abduction/retroduction in the narrow sense

"Peirce was the first [in history] to say straightforwardly that to deduction and induction, we must add a third (which he variously named abduction, hypothesis, retroduction) if we are to categorize properly what it is that makes science."

     Ernan McMullin, The inference that makes science, The Aquinas lecture 1992 (Milwaulkee, WI:  Marquette University Press, 1992), 85.
     Nonetheless, McMullin goes on to stress that what "makes science" is "the process as a whole":  "The process as a whole", of which abduction/hypothesis/retroduction as defined eventually by Peirce was for centuries the missing or at least unacknowledged part, "is the inference by means of which we transcend the limits of the observed, even the instrumentally observed" (92).  And that extremely complex "process as a whole" McMullin calls retroduction, "The product of [which] is [not law (itself an explanandum), but] theory or causal explanation" (93; cf. 2-3, 24, ).  Retroduction "is properly inference, since it enables one to move in thought from the observation of an effect to the affirmation, with [(contra Aristotle)] greater or lesser degree of confidence, of the action of a cause of a (partially) expressed sort", and it makes "an existence claim of [some] kind for [unobservable] theoretical entities. . . ."  In this way, realism (94, italics mine) becomes a characteristic of "the inference that makes science," becomes even a sine qua non of modern science.  (And that contra the scepticism of Hume (73-76).)
     "It is a far cry from the demonstrations of Aristotle to the retroductions of modern theoretical science.  Where they differ is, first, that retroduction makes no claim of necessity, and settles for less, much less, than definitive truth."  (According to McMullin (passim), it was the Aristotelian quest for "definitive truth" that held science up for centuries.)  "It can,  under favorable conditions, when theories are well-established, yield practical certainty.  Recent discussions of scientific realism show, however, how hedged this assertion must be. . . .  Second, the inductions that retroduction relies on are systematic and protracted, not simply a noticing of regularity.  Third, the observations from which retroduction begins are, for the most part, performed by sophisticated instruments; the limited scope and lack of precision of the human senses would never permit the range of retroduction that is necessary if the 'invisible realm', as Newton called it, is to be opened up.  Fourth, abduction [in this larger sense] often requires the introduction of new concepts and the testing of new language. . . . Finally, though retroduction is, indeed, an act of the intellect, as the epagoge underlying [Aristotelian] demonstration was asserted to be, it is exceedingly complex. . . . And it is open-ended. . . . It does not terminate in an act of intutitive [Aristotelian] insight wherein one sees that nature must be so" (96-97).

"Your grace, come back, Señor Don Quixote, I swear to God you're charging sheep!"

Douce Blog, Ashmolean

     Sancho Panza, in Miguel de Cervantes, Don Quixote I.xviii (trans. Edith Grossman (New York:  HarperCollins Publishers, Inc., 2003), 129).
     Cf. for sheer entertainment "the diverting adventure of the puppet master" in II.xxvi (pp. 628-636), in which, however, Don Quixote does manage to dispense justice inadvertently (II.xxvii (pp. 636 ff.)).

On the recurrence of the paschal feast

William Pye, Baptismal font,
Salisbury Cathedral (2008).

"God of everlasting mercy, who, in the very recurrence of the paschal feast kindle the faith of the people you have made your own, increase, we pray, the grace you have bestowed, that all may grasp and rightly understand in what font they have been washed, by whose Spirit they have been reborn, by whose Blood they have been redeemed.  Through. . . ."

God of everlasting mercy, who in the very recurrence of the paschal feast kindle from above the faith of the people consecrated to you, augment the grace you have given, so that all may with a worthy understanding comprehend in which font they have been washed, by which Spirit they have been reborn, by which blood they have been redeemed.  Through. . . .

     Collect for the Second Sunday of Easter (with patent reference to the epistle for year B, namely 1 Jn 5:1-8), taken word for word from the "Missa (in) die sabbato octava(e) paschæ" (Corpus orationum:  "Missa die sabbati octavam Paschae, post nomina") in the late 7th- or early 8th-century "Missale Gothicum" (so called). See, for example,

• Missale Gothicum (Vat. reg. lat. 317), ed. Leo Cunibert Mohlberg, Rerum ecclesiasticarum Documenta, Series major, Fontes 5 (Rome: 1961), 77;
• Missale Gothicum: das gallikanische Sakramentar-Cod. Vatican. Regin. Lat. 317-des VII.-VIII. Jahrhunderts, ed. Leo Cunibert Mohlberg (Ausburg: 1929), (a facsimile);
• "Missale Gothicum": a Gallican sacramentary (MS. Vatican. Regin. Lat. 317), ed. H. M. Bannister, vol. 1, Text and introduction, Henry Bradshaw Society 52 (London: 1917 [1916]), 89;
• Ancient liturgies of the Gallican church, ed. J. M. Neale and G. H. Forbes (Burntisland: 1855), 107;
• etc.

Corpus orationum no. 1268 (which cites only the early 8th-century Missale Gothicum (Cod. Vatic. Reg. Lat. 317)):
Deus misericordiae sempiternae, qui in ipso paschalis festi recursu fidem sacratae tibi plebis accendis, auge gratiam, quam dedisti, ut digna omnes intellegentia comprehendant, quo lavacro abluti, quo spiritu regenerati, quo sanguine sint redempti.

Mohlberg (1961), without variants:
Deus misericordiae sempiterne,
qui in ipso paschalis festae recursum
fidem sacratae tibi plebis accendis,
auge graciam quam dedisti,
ut digna omnes intellegencia conpraehendant,
quo labacrum abluti,
quo spiritu regenerati,
quo sanguine sunt redempti:
per.

Bannister, without variants:
Deus misericordiae sempiterne
qui in ipso paschalis festę recursum
fidem sacratę tibi plebis accendis
auge graciam quam dedisti
ut digna omnes intelligencia conpręhendant
quo labacrum abluti,
quo spiritu regenerati
quo sanguine sunt redempti
per. . . .

Neale and Forbes, without variants:
Deus misericordiæ sempiternæ,
qui in ipso paschalis festi recursu
fidem sacratæ tibi plebis accendis,
auge gratiam quam dedisti,
ut digna omnes intellegentia comprehendant,
quo lavacro abluti,
quo Spiritu regenerati,
quo sanguine sunt redempti.
Per. . . .

Those bloodthirsty medieval popes

"we believe in and confess one God, even if in a different way, and we praise and worship Him daily as the Creator of time and the ruler of this world. . . .
     ". . . For God knows [that] we love you purely for the honor of God and wish for your salvation and well-being in the present and in the future life, and with heart and mouth beseech God to conduct you, after a long course in this life, into the blessed bosom of the most holy Patriarch Abraham."

     Pope Gregory VII to an-Nasir ibn Alnas, the Hammadid emir of Bugie (Béjaïa), in 1076, as quoted by Peter Dinzelbacher, in his "Kritische Bemerkungen zur Geschichte der religiösen Toleranz und zur Tradition der Lessing'schen Ringparabel," Numen 55 (2008):  18 (1-26), which cites "Registrum 3, 21, Monumenta Germaniae Historica, Epp. Sel. 2, 287 f." (this passage on p. 288).  This, Dinzelbacher (citing pp. 545 ff. of The Crusades: an encyclopedia) points out, is the same Gregory who "planned a crusade."  Mere diplomacy-speak designed to secure the safety of Christians living in Bugie (citing Cowdrey, Pope Gregory VII, 1073-1085 (Oxford, 1998), 492 ff.; but "more positively" Gfrörer, Pabst Gregorius VII. und sein Zeitalter IV (Schaffenhausen, 1859), 581 ff., and Medieval Christian perceptions of Islam, ed. Tolan (New York, 2000))?  Maybe.  "but obviously Gregory himself was already able to conceive of a kind of natural religion."
     Nonetheless, I must not give the impression that Dinzelbacher, at least, would rehabilitate "'the'" Middle Ages more generally.  For "Neither Wolfram von Eschenbach nor Ramon Llull nor even Gregory VII" had any real impact, but were, rather, "untypical of their epoch".  Much more typical was, supposedly, Peter Comestor, who exclaimed, "funde sanguinem inimicorum" ("Shed the blood of the enemies of Christ") (18).  Indeed, it was only with the Renaissance, early modernity (which recovered the Stoic "conception of the equality of all men"), the Wars of Religion, and the Enlightenment (which stressed "that reason is common to all men") that a commitment to tolerance began to take hold (19 ff.).
     I began with Dinzelbacher's German, but here's the Latin, taken from MGH above:

"unum Deum, licet diverso modo, credimus et confitemur, . . . eum creatorem seculorum et gubernatorem huius mundi cotidie laudamus et veneramur.
     ". . . Scit enim Deus, quia pure ad honorem Dei te diligimus et salutem et honorem tuum in presenti et in futura vita desideramus atque, ut ipse Deus in sinum beatitudinis sanctissimi patriarchę Abrahe post longa huius vitę spatia te perducat, corde et ore rogamus."

"like a cow staring at a new gate"

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     "Joseph is for us not only an example of all the virtues, but also a lovely image of God for our eyes, so that we should know what God is.  The philosophers argue and try through speculation to break through to some kind of knowledge of God, even as Plato recognizes and acknowledges divine providence.  But all that is just external; it is not yet the knowledge that Joseph has, i.e., that God cares, and that he hears and helps the afflicted.  This Plato cannot say.  He remains within the limits of metaphysical thought, like a cow staring at a new gate [(Manet in cogitatione Metaphysica, wie ein kue ein newes thor ansihet)]."

     Martin Luther, Lectures on Genesis (1535-1545) at Gen 45:3 =WA 44.591.32-39 (where the German does not appear in italics), as trans. Mickey L. Mattox in his "From Lutheran to Catholic — justification and holiness," in Mickey L. Mattox and A. G. Roeber, with an afterward by Paul R. Hinlicky, Changing churches:  an Orthodox, Catholic, and Lutheran theological conversation (Grand Rapids, MI:  William B. Eerdmans Publishing Company, 2012), 48.  Cf. LW 8:16.  At this point, the WA indicates also WA 47.424.9 ("welche der Papst ansihet als ein kuh ein newe thor"), WA 50.533.34-35 ("wenn man die Buchstaben ansihet, wie eine kue das thor"), "u. ö."
     Does the switch into German indicate the appropriation of a saying, a commonplace?
     The image of the Pope as the one caught thus dumbfounded, and staring stupidly at the novum, is a scream. Luther as comic genius.  (But a genius who could serve the Gospel.)