gospel (n.)

Old English gōd (with a long "o") "excellent, fine; valuable; desirable, favorable, beneficial; full, entire, complete;" of abstractions, actions, etc., "beneficial, effective; righteous, pious;" of persons or souls, "righteous, pious, virtuous;" probably originally "having the right or desirable quality," from Proto-Germanic *gōda- "fitting, suitable" (source also of Old Frisian god, Old Saxon gōd, Old Norse goðr, Middle Dutch goed, Dutch goed, Old High German guot, German gut, Gothic goþs). A word of uncertain etymology, perhaps originally "fit, adequate, belonging together," from PIE root *ghedh- "to unite, be associated, suitable" (source also of Sanskrit gadh- "seize (booty)," Old Church Slavonic godu "favorable time," Russian godnyi "fit, suitable," Lithuanian goda "honor," Old English gædrian "to gather, to take up together").

Irregular comparative and superlative (better, best) reflect a widespread pattern in words for "good," as in Latin bonus, melior, optimus.

Sense of "kind, benevolent" is from late Old English in reference to persons or God, from mid-14c. of actions. Middle English sense of "holy" is preserved in Good Friday. That of "friendly, gracious" is from c. 1200. Meaning "fortunate, prosperous, favorable" was in late Old English. As an expression of satisfaction, from early 15c. Of persons, "skilled (at a profession or occupation), expert," in late Old English, now typically with at; in Middle English with of or to. Of children, "well-behaved," by 1690s. Of money, "not debased, standard as to value," from late 14c. From c. 1200 of numbers or quantities, "large, great," of time or distance, "long;" good while "a considerable time" is from c. 1300; good way "a great distance" is mid-15c.

Why then, can one desire too much of a good thing. ["As You Like It"]

As good as "practically, virtually" is from mid-14c.; to be good for "beneficial to" is from late 14c. To make good "repay (costs, expenses), atone for (a sin or an offense)" is from late 14c. To have a good mind "have an earnest desire" (to do something) is from c. 1500. Good deed, good works were in Old English as "an act of piety;" good deed specifically as "act of service to others" was reinforced early 20c. by Boy Scouting. Good turn is from c. 1400. Good sport, of persons, is from 1906. The good book "the Bible" attested from 1801, originally in missionary literature describing the language of conversion efforts in American Indian tribes. Good to go is attested from 1989.

Old English spell "story, saying, tale, history, narrative, fable; discourse, command," from Proto-Germanic *spellam (see spell (v.1)). Compare Old Saxon spel, Old Norse spjall, Old High German spel, Gothic spill "report, discourse, tale, fable, myth;" German Beispiel "example." From c. 1200 as "an utterance, something said, a statement, remark;" meaning "set of words with supposed magical or occult powers, incantation, charm" first recorded 1570s; hence any means or cause of enchantment.

The term 'spell' is generally used for magical procedures which cause harm, or force people to do something against their will — unlike charms for healing, protection, etc. ["Oxford Dictionary of English Folklore"]

In general terms, the belief underlying the use of spells is that the wish that they embody will be fulfilled, regardless of its goodness or badness, so long as the formula has been correctly pronounced. Broadly speaking, then, spell and prayer, like magic and religion to which they severally belong, can be distinguished by the nature of the intended purpose. [Enyclopaedia Britannica, 1941]

Also in Old English, "doctrine; a sermon; religious instruction or teaching; the gospel; a book of the Bible;" compare gospel. The 11c. glossaries give spel for Latin fabula.