The Codex Sinaticus and Codex Vaticanus have become known as the minority manuscripts because of the way they stand apart from the vast majority of manuscript evidence, known as the Textus Receptus. The letters of the two men, Wescott and Hort, clearly show us that one leaned toward Rome and the Vatican to the point of trusting in transubstantiation ( a Roman Catholic Dogma), and the other was friends with Darwin and the yearning for 'naturalistic' explanations for the origin of species. In much the same way as the early dinosaur bone diggers could promote their careers with a great find, Wescott and Hort would propell themselves to the fore by promoting their minority manuscripts as being older and therefore 'more accurate'. 

The Sinaitic manuscript was reportedly rescued from a wastebasket in a monastery on Mount Sinai by another German evolutionist theologian, Friedrich Tischendorf. The Orthodox monks evidently had long since decided that the numerous omissions and alterations in the manuscript had rendered it useless and had stored it away in some closet where it had remained unused for centuries. Yet Tischendorf promoted it widely and vigorously as representing a more accurate text than the thousands of manuscripts supporting the traditional Byzantine text. Furthermore, he assumed that it came from about the fourth century, but he never found any actual proof that it dated earlier than the 12th century.

A similar mystery applies to the famous Vatican manuscript, which had been kept in seclusion in the Vatican Library since 1480 or earlier, though no one seemingly knows for sure when it was originally written or how it was acquired by the Vatican. Again, it was only conjectured to date from around the fourth century. Tischendorf learned of its existence and again was instrumental in promoting its antiquity and superiority to the Textus Receptus. The Vatican manuscript, for example, leaves out most of Genesis as well as all of Revelation, in addition to the pastoral epistles of Paul, 33 psalms, and over a third of Hebrews.

Almost all of the new versions of the New Testament are based on what is known as the Westcott-Hort Greek text, or some modification thereof (such as the Nestle-Aland text), whereas the King James is based largely on what is known as the Received Text (also called the Textus Receptus or the Byzantine Greek text). As far as the Hebrew text of the Old Testament is concerned, the King James is based on the Masoretic text, while the modern versions rely somewhat on the Masoretic but also on the Septuagint, the Latin Vulgate, the Dead Sea Scrolls, and various others, especially the Kittel Hebrew reference text, Biblia Hebreice, in its "Stuttgart" edition.

The Masoretic text was compiled from the ancient manuscripts of the Old Testament by the Masoretes, who were groups of Hebrew scholars dedicated to guarding and standardizing the traditional Hebrew text as "handed down" (the basic meaning of "Masoretic") from the earlier Hebrew scribes, who had in turn meticulously copied the ancient Hebrew manuscripts, scrupulously guarding against error. There seems no good reason why the Masoretic text as preserved and codified in its present form by about 600 A.D., which has served as the basis for the King James translation, should not continue to be accepted as the most accurately preserved Old Testament portion of the Bible.

Most scholars would agree that neither the Greek Septuagint nor the Latin Vulgate are comparable to the Masoretic Text in accuracy or reliability. As far as the Hebrew text changes proposed by Rudolf Kittel are concerned, it is worth noting that Kittel was a German rationalistic higher critic, rejecting Biblical inerrancy and firmly devoted to evolutionism. The Dead Sea Scrolls were produced by a heretical Jewish sect called the Essenes, but for the most part they do agree with the standard Masoretic Text.

There are a few other old manuscripts, even including fragmentary Greek papyri, whose textual character seems to conform more to the Sinaiticus and Vaticanus readings than to the Textus Receptus. These all have been traced, by liberal and conservative scholars alike, to a probable source in Alexandria, Egypt, in the second or third century. At that time, Alexandria was a great center of both philosophical and theological scholarship, including a relatively large population of both Jews and Christians.

The most influential man among the Christian community of Alexandria was the learned Origen, and it is believed by many that he was largely instrumental in developing the so-called "Alexandrian" text of the New Testament, of which the Vatican and Sinai manuscripts are representative, in contrast to the "Byzantine" text, from which the Textus Receptus has largely come. It is barely possible, some think, that Origen may also have been involved in developing the final form of the Septuagint translation of the Old Testament.

Origen's views of theology and Biblical interpretation were heretical in respect to numerous key doctrines. Like modern theistic evolutionists, he felt constrained to harmonize Christianity with pagan philosophy, especially that of Plato and the Stoics. This led him into excessive allegorization of Scripture, especially Genesis, and into denigrating the actual historical records of the Bible, even that of the bodily resurrection of Christ, as well as the literal creation of the world.

Whether or not Origen and his associates were first responsible for the differences in the Alexandrian text from the Byzantine, the fact remains that significant differences do exist, and that practically all modern English translations have been heavily influenced (via Westcott/Hort, etc.) in favor of the former, whereas the King James translation has its basis primarily in the latter.

The differences are minor in many cases, but it is true that far too many do involve significant dilution of even such basic doctrines as Biblical inerrancy, the perfect divine/human nature of Christ, and the Trinity. On the other hand, they certainly do not eliminate these doctrines, so it is still happily possible to discern these doctrines and to find the true gospel and way of salvation in almost any of the new texts or translations.

One of the serious problems with almost all modern English translations is that they rely heavily on Hebrew and Greek manuscripts of the Bible developed by liberals, rationalists, and evolutionists, none of whom believed in the verbal inspiration of the Bible. Are we to believe that God would entrust the preservation of His eternal Word to men such as these? Would He not more likely have used devout scholars who believed in the absolute inerrancy and authority of the Bible?

Many fine points of English grammar commonly used in 1600 for example, we forget that "thee," "thou," and "thine" were used to express the second person singular; with "you," "ye," and "yours" reserved for second person plural. Today we use "you" indiscriminately for both singular and plural, thereby missing some of the precise meaning of many texts of Scripture. The same applies to the "th" and "st" endings on verbs associated with second-person pronouns; they also contribute significantly to the musical quality of the language, especially as used in the King James Bible.

Those who defend the modern bible versions believed that Received Greek Text is interpolated with words from the translators whereas KJV supporters said that the scholars Drs. Wescott & Hort deleted the verses or word of God to produce the manuscript known as the Critical Text. However, Dr. Frank Logsdon has come to his senses that Critical Text contains absolutely frightening deletions of verses or words. He also showed open support for KJV. 

Based on Oxford Dictionary on the definition for the word "Study", there is no mention of its equivalent to an old English meaning of "be diligent to" in NKJV and "Do your best" in NIV. I do not know Greek word for "study" but the key to better understanding of the scriptures is employing common English word in the right context. The true translators are submitted to the guidance of the Holy Ghost to use the right choice of word. I do not think the common word "study" is old and need to be changed. Reading the context of 2 Timothy 2:14-15:
Of these things put them in remembrance, charging them before the Lord that they strive not about WORDS to no profit, but to the subverting of the hearers. STUDY to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the WORD of TRUTH.  

Thus it is referring to the study of the word of truth, i.e., God's word which is literally the Bible.