Due to Jewish thought absorbing Greek culture prior to Jesus coming on the scene in Israel in 29 C.E., the name of God, Jehovah, was used little or none. At some point a superstitious idea arose among the Jews that it was wrong even to pronounce the divine name (represented by the Tetragrammaton). Just what basis was originally assigned for discontinuing the use of the name is not definitely known. Some hold that the name was viewed as being too sacred for imperfect lips to speak. Yet the Hebrew Scriptures themselves (commonly called the Old Testament) give no evidence that any of God’s true servants ever felt any hesitancy about pronouncing his name. Non-Biblical Hebrew documents, such as the so-called Lachish Letters, show the name was used in regular correspondence in Palestine during the latter part of the seventh century B.C.E.
Another view is that the intent was to keep non-Jewish peoples from knowing the name and possibly misusing it. However, Jehovah himself said that he would ‘have his name declared in all the earth’ (Ex 9:16; compare 1Ch 16:23, 24; Ps 113:3; Mal 1:11, 14), to be known even by his adversaries. (Isa 64:2) The name was in fact known and used by pagan nations both in pre-Common Era times and in the early centuries of the Common Era. (The Jewish Encyclopedia, 1976, Vol. XII, p. 119) Another claim is that the purpose was to protect the name from use in magical rites. If so, this was poor reasoning, as it is obvious that the more mysterious the name became through disuse the more it would suit the purposes of practicers of magic.
When did the superstition take hold? Just as the reason or reasons originally advanced for discontinuing the use of the divine name are uncertain, so, too, there is much uncertainty as to when this superstitious view really took hold. Some claim that it began following the Babylonian exile (607-537 B.C.E.). This theory, however, is based on a supposed reduction in the use of the name by the later writers of the Hebrew Scriptures, a view that does not hold up under examination. Malachi, for example, was evidently one of the last books of the Hebrew Scriptures (Old Testament) written (in the latter half of the fifth century B.C.E.), and it gives great prominence to the divine name.
Many reference works have suggested that the name ceased to be used by about 300 B.C.E. Evidence for this date supposedly was found in the absence of the Tetragrammaton (or a transliteration of it) in the Greek Septuagint translation of the Hebrew Scriptures, begun about 280 B.C.E. It is true that the most complete manuscript copies of the Septuagint now known do consistently follow the practice of substituting the Greek words Ky´ri·os (Lord) or The·os´ (God) for the Tetragrammaton. But these major manuscripts date back only as far as the fourth and fifth centuries C.E. More ancient copies, though in fragmentary form, have been discovered that prove that the earliest copies of the Septuagint did contain the divine name.
One of these is the fragmentary remains of a papyrus roll of a portion of Deuteronomy,(Deut 18:15,16) listed as P. Fouad Inventory No. 266. It regularly presents the Tetragrammaton, written in square Hebrew characters, in each case of its appearance in the Hebrew text being translated. This papyrus is dated by scholars as being from the first century B.C.E., and thus it was written four or five centuries earlier than the Codex Alexandrinus of the 5th century C.E., which had replaced the Tetragrammaton with KC and KY, abbreviated forms of the Greek word Kyrios ("Lord"). Thus, in the centuries following the death of the last apostle, John, in about 100 C.E., the Divine name of Jehovah was eventually replaced by "Lord". However, some Bibles have reestablished God's name of Jehovah within their pages, as was in the most ancient manuscripts, such as the New World Translation, the American Standard Version, Young's Bible, and Darby's Bible.(see also the online interlinear, Scripture4all)
(Source of some of the information - Insight On the Scriptures, Vol 2, pg 5)
