The blood that laves the stars

"mite corpus perforatur, sanguis unde profluit;
terra, pontus, astra, mundus quo lavantur flumine!"

gently [his] body is pierced through,

     whence blood flows forth;

in which stream the earth, the sea, the stars,
     the universe [(or human race)] are washed.

     Venantius Fortunatus, "Pange lingua gloriosi proelium certaminis" (Poems 4.2), stanza 7 (in part), as reproduced (but not translated) in the current Roman missal, at Good Friday.  In the critical edition in MGH, Auctores Antiquissimi 4 (1881-1885), pp. 27-28, this comes out as

"mite corpus perforatur, sanguis unda profluit;
terra, pontus, astra, mundus quo lavantur flumine."

gently [his] body is pierced through,
     [and] blood, a wave [of it (or blood, rising in waves)], flows forth;
in which stream the earth, the sea, the stars
     the universe [(or human race)] are washed.

See also the modern critical edition:  Poèmes, ed. Reydellet, Collection des Universités de France, vol. 1 (Paris:  Les Belles Lettres, 1994), p. 51:

"Mite corpus perforatur, sanguis unda profluit,
terra pontus astra mundus quo lauantur flumine."

"taking the form of a slave"

Grünewald

"The ignominy of a public trial is a miserable thing,—the deprivation of a man's property by way of penalty is a miserable thing,—exile is a miserable thing; but still, in all these disasters some trace of liberty remains to one. Even if death be threatened, we may die free men; but the executioner, and the veiling of the head, and the mere name of the [cross (crucis)], should be far removed, not only from the persons of Roman citizens—from their thoughts, and eyes, and ears. For not only the actual fact and endurance of all these things, but the bare possibility of being exposed to them,—the expectation, the mere mention of them even,—is unworthy of a Roman citizen and of a free man. Does not the kindness of their masters at one touch deliver our slaves from the fear of all these punishments; and shall neither our exploits, nor the purity of our past life, nor the honours which you have conferred on us, save us from the scourge, from the hangman's hook, and even from the dread of the [cross (crucis)]?"

     Cicero, Pro C. Rubirio oratio 5.16, trans. C. D. Yonge, who used for "crux" "gibbet," not "cross."  A passage cited (whether accurately or not) as proof of the claim that "Crucifixion was not only the most agonizing [(atroce)] of punishments/tortures, 'summum supplicium' (Digest, De poenis 48.19.28), it was also the most degrading, that of slaves, 'servile supplicium' (Tacitus, Historiae 4.11), and that of great criminals; normally one did not crucify a Roman citizen (Cicero, Contra Verrem 2.5.64 (165), 66).  The cross, 'arbor infelix' (Livy, Historia 1.26.6; Cicero, Pro C. Rubirio oratio 4.13), was synonymous with horror and abjection" (Dictionnaire de spiritualité, sv Folie de la croix I, by Donatien Mollat, vol. 5 (1964), col. 639).  Latin from here.

Christ the trader

"He had no power of himself to die for us. . . .  Of ourselves we had no power to live, nor did he of himself have the power to die.  Accordingly, he effected a wonderful exchange with us, through mutual sharing: we gave him the power to die, he will give us the power to live."

     St. Augustine, Sermo 218C =Sermo Guelferbytanus 3.1 (Good Friday, 412/415), trans. Liturgy of the hours.  SC 116 (1966):  (200-208) =PLS 2 (), col. 545.  WSA III.6 =Sermons on the liturgical seasons, trans. Edmund Hill (1993), 194:

he would not have in himself the wherewithal to die for us, unless he had taken mortal flesh from us.  That was how the immortal one was able to die, that was how he wished to bestow life on mortals; aiming later on to give us shares in himself, having first of all himself taken shares in us.  I mean, we had nothing of our very own by which we could really live, and he had nothing of his very own by which he could really die.  Accordingly, he struck a wonderful bargain with us, a mutual give and take:  ours was what he died by; his was what we might live by.

Non enim habebat in semetipso unde moreretur pro nobis nisi moralem carnem sumpsisset ex nobis.

Sic inmortalis mori potuit, sic uitam donare mortalibus uoluit, participes sui postea facturus quorum esset prior particeps factus.

Nam nec unde uiueremus nos habebamus de nostro nec unde moreretur ille de suo; mirum proinde nobiscum egit mutua participatione commercium:  nostrorum erat unde mortuus est, illius erit unde uiuamus.

SC 116, ed. Suzanne Poque (1966), 200, 202.  A footnote here:  "One sees sketched here the theme of the Christus mercator, cf. Introduction, p. 16.  In S[ermo] Denis 5[.5 =sermon no. 375B.5], the same considerations are placed in the very mouth of Christ [himself]", as translated here by Edmund Hill O.P. (WSA III/10 (Hyde Park, NY:  New City Press, 1995), 335).  Unfortunately, this is considered a sermon of doubtful authenticity:

'I had no means of dying; you, man, had no means of living.  I took from you the means by which to die for you; now you take from me the means by which to live with me.  Let's strike a bargain; I give to you, give something to me.  From you I receive death; from me receive life.  Bestir yourself; notice what I am giving, what I am receiving.  Though sublime in heaven, I received from you the form of a servant (Phil 2:7).  While I am your health , what I received from you were wounds; while I am your life, what I received from you was death.  While I am the Word, I became flesh, in order to be able to die.  I had no flesh with the Father; it was from your lump that I received what I would spend for you. . . . I took flesh from you, in which to die for you; receive the life-giving spirit from me, with which to live with me.  In a word, I died from what is yours; see to it that you live from what is mine.'