"conduct her along the narrow byways of time to the eternal joy of your kingdom"

"With mighty hand and outstretched arm you led your people Israel through the desert.  Now, as your Church makes her pilgrim journey in the world, you always accompany her by the power of the Holy Spirit and lead her along the paths of time to the eternal joy of your Kingdom [(eamque per temporis semitas in gaudium aeternum regni tui conducis)] through Christ our Lord."

     "Eucharistic Prayer for Use in Masses for Various Needs II:  God Guides His Church along the Way of Salvation," Missale Romanum, 3rd typical edition (CTS new daily missal, people's edition (London:  Catholic Truth Society, 2012), 1136|1137).  The phrase "per temporis semitas" is very close to the "in temporis semitis" of the post-synodal apostolic exhortation of John Paul II Pastoris gregis (On the Bishop, Servant of the Gospel of Christ for the Salvation of the World) 12, 16 October 2003:

the Bishop will be able to show his brothers and sisters that he is their father, brother and friend only if he has entered the dark yet luminous cloud of the mystery of the Father, Son and Holy Spirit. Radiant with the light of the Trinity, he will be a sign of the merciful goodness of the Father, a living image of the love of the Son, and transparently a man of the Spirit, consecrated and sent forth to lead the People of God along the paths of history on their pilgrimage to eternity [(ut Dei Populus in temporis semitis ad aeternitatem peregrinans ducatur)].

I was unable to turn "temporis semit*" up in the Vulgate at Bible Gateway, and indeed this Eucharistic Prayer appears to be a post-Vatican II composition.  In Mt 7:14 the phrase is "arcta via" ("narrow . . . way").
     For some moving images, see the amazing series of photographs by Amos Chapple in Alan Taylor, "The shepherds of the Tusheti Mountains," The Atlantic, 31 October 2017.

The question is how to become "capable and fit" for such friendship

"Angels have not, nor affect not other knowledge of one another, then they lift to reveal to one another.  It is then in this onely, that friends are Angels, that they are capable and fit for such revelations when they are offered."

     John Donne to S^r H[enry]. G[oodyer]., Letters to severall persons of honour (London, 1651), 109-110, as quoted by David Marno in Death be not proud:  the art of holy attention (Chicago:  The University of Chicago Press, 2016), 90.

"'if your right hand causes you to sin'"

"all they that continue in their evill wayes. . . . must depart:  how far?  first, they must be avoided, Declinate, saith S. Paul, I beseech you brethren, marke them diligently which cause division and offences, and avoid them.  And this corrects our desire in running after such men, as come with their owne inventions, Schismaticall Separatists, Declinate, avoid them; if hee be no such, but amongst our selves, a brother, but yet a worker of iniquity, If any one that is called a brother, be a Fornicator, or covetous, with such a one eate not.  If we cannot starve him out, wee must thrust him out; Put away from among you, that wicked man.  No conversation at all is allowed to us, with such a man, as is obstinate in his sin, and incorrigible; no not to bid him God speed, For he that biddeth him God speed, is partaker of his evill deeds.  In this divorce, both the generality, and the distance is best exprest by Christ himselfe, If thine eye, thine hand, thy foote offend thee, amputandi & projiciendi, with what anguish or remorse soever it be done, they must bee cut off, and being cut off, cast away; it is a divorce and no super-induction, it is a separating, and no redintegration.  Though thou couldest be content to goe to Heaven with both eyes, (thy selfe, and thy companion) yet better to goe into Heaven with one, thy selfe alone, then to endanger thy selfe to be left out for thy companions sake."

     John Donne, Sermon on Ps. 6:8-10, April, May, or June of 1623, John Donne Sermons 6.

"a firm and certain knowledge"

"As attention exercises, [Donne's poems] are aimed at allowing the speaker to think a religious doctrine with a certainty that is subjective and existential.  In other words, they are meant to create a very specific kind of knowledge:  faith."

     David Marno, Death be not proud:  the art of holy attention, Class 200:  new studies in religion (Chicago:  The University of Chicago Press, 2016), 33.  The headline comes from Calvin (whom, by the way, Marno has just quoted on p. 25).

The more of God, the more of me

"Today we glorify God by being humble; in heaven it is our glory that will be his praise, it is our glory that will glorify him."

"Aujourd’hui, nous glorifions Dieu en étant humbles; au ciel, c’est notre gloire que sera sa louange, c’est notre gloire qui le glorifiera."

     Pierre-Marie Hombert, Gloria gratiae:  se glorifier en Dieu, principe et fin de la théologie augustinienne de la grâce, Collection des études augustiniennes, série antiquité 148 (Paris:  Institut d'études augustiniennes, 1996), 552, as quoted by Augustine specialist Gerald Bonner, in his review (Journal of theological studies 49, no. 2 (October 1998):  857 (855-858)), emphasis mine.  The pattern here is, of course, Jesus himself,

who . . . did not count equality with God a thing to be grasped, but . . . humbled himself and became obedient unto death, even death on a cross. Therefore God has highly exalted him. . . .

"Our predestination [is] in the predestined Christ".  This is "the keystone of Augustinian theology as a whole" (Hombert, 448).  "the elect—and Augustine never ceased to regard any human being as being potentially one of the elect, so long as breath remained in the body—are glorified in Christ and so should glorify God, through whom, and only through whom, they are glorified" (Bonner, 857).
     The humility of God is the glory of man.

No easy, "centering," candlelit, feel-good exercise

"the meditative reading of Scripture was understood by the first generations of monastic Christians to be an arduous physical activity, undertaken as penance and ascesis.  By the labor of reading [(lectio divina)], the struggling ascetic might learn to purify his troublesome will and fortify himself against the unwholesome distractions of an incessant mental chattering (the logismoi, interpreted as demonic promptings).
". . . Meditative reading was [only] the first step in a long pilgrimage from the 'region of unlikeness' towards the condition in which the divine image would shine forth fully restored."

     Carol Zaleski, "Attending to attention," in Faithful imagining:  essays in honor of Richard R. Niebuhr, ed. Sang Hyun Lee, Wayne Proudfoot, and Albert Blackwell (Atlanta:  Scholars Press, 1995), 140 (127-149).  Zaleski gives a handy list of her authorities.

"A table without a remembrance of God is indistinguishable from a feeding-trough."

Source

Τράπεζα μὴ ἔχουσα μνήμην Θεοῦ, φάτνης ἀλόγων οὐδὲν διενήνοχεν.

     Leontius of Byzantium, Rerum sacrarum 2, On dinner (Περὶ δείπνου), PG 86, col. 2077B.  I was put onto this by Hermann Josef Sieben, "ΜΝΗΜΗ ΘΕΟΥ," Dictionnaire de spiritualité 10 (1980), 1412 (1407-1414).