The Bible uses many terms and descriptions for God, one of the most prominent of which is Yahweh. This is the personal name by which the Israelites referred to him.
The name is generally thought to be based on the Hebrew verb for “to be” (HWH), though its precise meaning is unclear. Proposals include “I am the One Who Exists,” “He who causes to be,” and “I am/will be present.”
Because the Hebrew writing system did not originally include vowels, the name is written in the Hebrew Bible using only four consonants: YHWH. These are often referred to as the tetragrammaton—a Greek term meaning “the four letters.”
Because of its lack of vowels, the word’s pronunciation has been a subject of debate. However, based on various lines of evidence, Yahweh is regarded as the most likely pronunciation.
The issue is complicated by the fact that, in the centuries just before Christ, pious Jews became hesitant to pronounce the name. The Ten Commandments warn: “You shall not take the name of the Lord your God in vain; for the Lord will not hold him guiltless who takes his name in vain” (Exod. 20:7; cf. Deut. 5:11). Many Jews decided that, to avoid the possibility of misusing the divine name, they would not pronounce it at all.
Consequently, they began to substitute other words for it, such as Adonai—a Hebrew term meaning “my lord.” Consequently, when the Hebrew Bible was translated into Greek, the resulting Septuagint version generally used terms like the Greek word Kurios (“Lord”) where the tetragrammaton appeared in Hebrew. This pious custom passed over into Christian circles, and when the authors of the New Testament quote from the Old Testament, they generally use Kurios where the Hebrew has YHWH.
The substitution of Kurios for YHWH in the Septuagint and the New Testament is why most English Bibles have “LORD” wherever the divine name appears in the Old Testament. (The small caps tell you it is YHWH rather than Adonai in the original.)
In Jewish circles, the custom of not pronouncing the divine name continued to be used, and when the Hebrew writing system began to include vowels (written as small marks or “points” above, below, or inside the consonants), the scribes had to decide whether to use the vowel points for Yahweh.
It was decided they wouldn’t. Instead, they wrote the consonants YHWH using the vowel points for Adonai as a reminder to Jewish lectors to say “Adonai” instead of “Yahweh.” This custom of writing the consonants of one word with the vowels of another is where we get the English word “Jehovah.” In Latin, “YHWH” had become “JHWH,” and when combined with the vowels of Adonai—a, o, and a—it became “Jahowah,” which then became the English “Jehovah.” Some have argued that this usage began in the Christian community as early as the twelfth century, though it is often traced to 1518, when Petrus Galantinus, O.F.M.—the confessor of Pope Leo X—published a book that popularized it.
From a theological point of view, it is clear that God does not have a problem with people using the name, for the Israelites did so until the contrary custom arose in the centuries just before Christ. The custom thus was not a matter of divine law.
In fact, the idea that making a substitution would shield you from misusing God’s name is wrong. If you substitute “Adonai” or “Kurios” and then go on to profane that word, God still knows you’re misusing a reference to him.
However, it’s also clear that God doesn’t consider it mandatory for Christians to use the divine name. That’s obvious in the case of “Jehovah,” since this form didn’t even exist in biblical times, but it’s also clear that the same applies to “Yahweh,” since the authors of the New Testament regularly use Kurios when the Old Testament has YHWH.
The practice of using the divine name is thus sanctioned by the many books of the Old Testament that do use it, and the practice of using a substitute is sanctioned by the books of the New Testament, which follow that custom.