Crist

Crist, a translation of "Christ", is the name of a set of three 10th century Old English poems that concern Jesus Christ, found in the Anglo-Saxon "Exeter Book". Its three constituent poems are simply named Christ I, Christ II (which was known to be written by the poet Cynewulf), and Christ III.

Relevance
The character Eärendil, who in the First Age was responsible for the intervention of the Valar upon Morgoth and Morgoth's subsequent defeat, originated from a seeming revelation Tolkien experienced in 1913 when he first read a particular line from Christ II:

 Crist, éala éarendel engla beorhtast ofer middangeard monnum sended

In English, this is closest to meaning Hail Earendel, brightest of angels, sent over middle-earth to mankind! Tolkien is cited to have said that upon reading it he "...felt a curious thrill as if something had stirred in me.....There was something very remote and strange and beautiful behind those words, if I could grasp it, far beyond the ancient English." This moment and inspiration is noted by Tolkien scholars to have been important in the first shaping of the legendarium of Middle-earth as a mysterious philological realization, or even in fact to have been the legendarium's first cause. It prompted Tolkien's writing of the poem initially entitled "The Voyage of Éarendel the Evening Star", of which he would write five successive versions, starting in September of 1914. From this poem would stem The Tale of Eärendel which Tolkien later composed, also in multiple schemes and emendations, but never completed. Much later it had evolved into the final climax of Quenta Silmarillion, "Of the Voyage of Eärendil and the War of Wrath". The Tale became the fifteenth of the Lost Tales in order of publication - and it was implied by its narrator, the character Gilfanon, to be the great culmination of all tales that preceded it.

The two quoted lines from Christ II also inspired Tolkien's use of the very term "Middle-earth".