Why do they do it? The reasons are various, but these seem to be the chief ones, listed in ascending order of evil:
(1) An attempt to improve the poetry qua poetry, by smoothing over rough meter or ill-considered syntax. Among translations, this is often by mixing versions by different translators. John Mason Neale was a brilliant translator, but we will not tell you that on a particular verse or image he cannot be excelled by, say, Edward Caswall.
To be honest, this "improvement" isn't so very wicked, and may even result in better hymns. (Poetic syntax can certainly be a problem. A friend recalls visiting a parish which proudly displayed a banner, handcrafted by its children, featuring this from A Mighty Fortress : "On earth, he has no equal." Our friend remarks, "I didn't know how to tell them that this is about the Devil.") Yet, on the other hand, the Great Hymn Massacre (in Part 2) was just such an effort.
(2) An attempt to make archaic language comprehensible to modern people. This, of course, assumes that modern people are too blooming stupid to recall the meaning of "thee" or "thou," something which is not the case in our experience. Far worse, it may result in the sweeping aside of Biblical imagery deemed "obscure" to the modern churchgoer.
(3) An attempt to change to change the poem's meaning, so that it reflects the theological biases not of its author, but of its editor. This is the most mischievous of all, and it takes several forms:
(a) Abbreviation. Many hymns are so very long that all their stanzas cannot easily be printed in a hymnal, especially given the perverse obligation that some worship leaders feel to play, sing, or require to be sung every word that they see before them. The Stabat Mater has 20 stanzas, and they form a coherent whole; but five is ample for congregational use, unless one intends to structure one's entire devotion around it. (O Sacred Head is no piker, with 11 stanzas -- of which only four appear in either the LBW or ELW).
Abbreviation may be a necessary evil, but it is still an evil. By printing dismembered hymns, the editors deprive congregations of the ability to perceive the author's full intention. They also make it more difficult for worship leaders who may be so inclined to use the full text -- for example, to actually structure one's Good Friday observance around the Stabat Mater or O Sacred Head.
(b) Selection. Worse yet, the decision to chop out stanzas inevitably urges the question of which stanzas -- and which images -- shall go or stay. This is typically guided by the theological views of the editors. For example, we once noticed that when printing The Church's One Foundation, Baptist hymnals omit the lines about "each new-born soldier of the Crucified," for fear that it will confuse the antipaedobaptist faith. Likewise, the newest Lutheran hymnal, ELW, omits the bit about "conquering ranks," perhaps from squeamishness about making Jesus' humblest sheep remember their coreligionists' role in two wars for world conquest.
Mind you, Lift High is practically a test case in mucking-about. As written, in 1887, it was apparently quite different from the rewritten version that first saw print in a 1916 hymnal. We're not sure of the differences, because all our good reference books are packed away. But in modern hymnals, even the re-written version is rarely printed whole; of twelve brief stanzas, five or six are usually printed.
Sadly, this means that congregations rarely have the chance to offer this prayer: "Set up your throne, that earth's despair may cease / beneath the shadow of its healing peace," much less the frighteningly universalist line about "thy Cross which doth for all atone." Maybe Rob Bell's people can sing that one.
(c) Substitution. This, to be sure, is where the mischief is worst -- where sins of omission become sins of commission, and where images and ideas for which the editor does not care are simply replaced with others more fashionable. A lot of substitution is made in quest of gender-neutrality, about which one feels however one feels. We will only observe that a hesitance to call Jesus "Lord" is theologically problematic in the extreme. But that is by no means all, nor even the worst, of it.A popular GIA hymnal changes a key line in Amazing Grace from "that saved a wretch like me" to "that saved and set me free." Oy. Need we observe that this undermines the entire narrative upon which the hymn is built? From a Pauline story of personal confession and restoration, it is transformed into an Exodus story of passive deliverance from one external power to another. Never mind the backstory, of John Newton's own wretchedness as a slave-trader, nor the fact that the words the editors have changed are among the most famous in all of English hymnody.
Mind you, it does not pay to be overly alarmist about such matters. For example, we can imagine some pastor -- okay, one particular pastor, a fellow with whom we once worked who is given to perpetual lamentation over the decadence of his church -- holding his head in his hands and crying that ELW has changed "O Wondrous Type, O Vision Fair" to "O Wondrous Image, Vision Fair." We can practically hear him going on about how, by removing the word type, the editors have betrayed a central commitment of patristic and medieval Biblical exegesis.
But he'd be mistaken. In fact, the Latin hymn Coelestis formam gloriae isn't explicitly typological to begin with. Neale introduces the word in his 1854 translation, which was not originally the one found in most hymnals: "A type of those bright rays on high ...." It was the 1861 hymnal editors who mucked about with Neale, and produced the compound version most of us know.
Still and all, we do not support this mucking about. If you don't like the hymn, don't sing it. If you do like it, but not all, sing the parts you like. But the custom of chopping hymns up, selectively rewriting them, and leaving out the bits that bother you (but which may be somebody's favorite) strikes us us unmannerly, a poor way to treat the poets and translators who have done their best and produced something to which they, often at least, have been proud to affix their names.
Now, not all editors have the good manners to indicate that they have thus mucked, and we are grateful to those who have worked on our Lutheran hymnals over the generations for choosing the path of manners. We only wish that they wouldn't choose it quite so often.