Q. Why do Christians, but not Jews, call God “Jehovah”?A. In the Tanach (Hebrew Bible) the authentic name of God is spelt Y-H-V-H. The text has no vowels, only consonants. It seems certain that the name derives from the root H-V-H, “to be”, and points to the uniqueness of God’s being.
In ancient Israel the name was pronounced only on the Day of Atonement and only by the high priest, and the correct pronunciation was not known to the people as a whole. When the Temple ritual was suspended nearly two thousand years ago, the secret was lost for ever (unless the Almighty chooses to reveal it again). No-one can therefore be certain how to vocalise the name, and no-one is entitled to guess.
Hebrew grammar would allow for at least two possibilities – a vocalisation that would indicate “He who is”, or one that would denote “He that causes (all) to be”.
Christian tradition was quite ungrammatical in using the form Jehovah. No such pronunciation fits in with any of the rules of Hebrew. What happened was that Jews piously substituted for the name Y-H-V-H the title AD-ON-AI, “My Lord”. They could not remove the original consonants of the name from the Scriptures, but when printed or handwritten books began to insert vowel points in the texts as an aid to reading, they added the vowels of the substitute title to the original name as a sort of coded clue to help the reader.
The word therefore looked something like Jehovah, but no Jew or Hebrew scholar would ever read it as such.