'Jehovah' is a rendering of God's name that has been recognized for centuries. In the original Hebrew text, the name appears nearly 7,000 times. Its use throughout the Scriptures far outnumbers that of any of the titles, such as "Sovereign Lord" or "God," applied to Him.
Here are the four instances the name "Jehovah" is used in the King James Bible:
In Hebrew, God's name appears as four consonants: יהוה. These consonants are transliterated YHWH and are known as the Tetragrammaton.
At some point a superstitious idea arose among the Jews that it was wrong even to pronounce the divine name. Evidently, later copyists kept to following the tradition of eliminating the distinctive name of God by replacing it with Ky´ri·os and The·os´ ("LORD" and "GOD"). Unfortunately, because of the superstitions and traditions (things which Jesus condemned - Mt. 15:1-9) concerning the Divine Name, God's name was generally removed from the texts altogether.
Does the Name 'Jehovah' Belong in the New Testament?
Yes, most of the physical evidence found in existing N(ew) T(estament) manuscripts does not support "Jehovah" in the New Testament. But what makes such a difference is the belief that BOTH "Testaments" are the word of God and must not contradict each other in important areas of knowledge.
We can accept both "Testaments" as the inspired word of God and still see understandable differences occurring between the two, but not basic contradictory differences. For example, we know how and why animal sacrifices to God have been done away with. It has been carefully, logically explained in the NT and, therefore, does not contradict the OT teachings where such sacrifices were required (essential). But where is the careful, logical explanation that shows that the necessary knowledge and use of God's name (as clearly acknowledged by word and example throughout the OT) was done away with in the NT?
It's not there. How can it be that God reveals His personal name and commands that it be publicly acknowledged and used forever by His servants (and they respectfully do so for over a thousand years) and then, for no scriptural reason, His worshipers suddenly begin refusing to use that name and even hide it?
Therefore, if we are to keep the Scriptures from terribly contradicting themselves in an extremely important area, we must conclude that either the OT scriptures are wrong or the oldest available NT manuscripts and fragments (at least those which actually contain places that quote from the OT where "YHWH" was originally used) are copies that have been CHANGED FROM THE ORIGINAL. Since the name of God being used as YHWH even in everyday life is attested to by archaeological findings back to the 8th century B. C. at least, we are really forced to conclude that, yes, the existing NT manuscripts are terribly wrong in this particular area.
And even with these changes, the Name has not been entirely left out of the N.T. since Revelation 19:1, 3, 4, 6 still retains "Alleluia":
"ALLELUIA, the Greek form (Revelation 19:1, 3, 4, 6) of the Hebrew Hallelujah = Praise ye *JEHOVAH*, which begins or ends several of the psalms (106, 111, 112, 113, etc.)." – Easton's Bible Dictionary, Thomas Nelson Publ., 1897.
For more, see:
Should the Name Jehovah Appear in the New Testament? (THE WATCHTOWER 2008-08-01; JW.ORG)
"Jehovah" in The New Testament (Category) (Defend Jehovah's Witnesses)
God's Name (Category) (Defend Jehovah's Witnesses)
The New World Translation and the Restoration of God's Name 237 Times in the New Testament (Defend Jehovah's Witnesses)
Hallelujah / Jah - The Removal of God's Name and Why "Hallelujah" Remained (Defend Jehovah's Witnesses)
Should the name Jehovah not be used because it is said that the letter "J" isn't in Hebrew? (Defend Jehovah's Witnesses)