In Jewish thought, a name is not merely an arbitrary designation, a random combination of sounds. The name conveys the nature and essence of the thing named. It represents the history and reputation of the being named. Because a name represents the reputation of the thing named, a name should be treated with the same respect as the thing's reputation. For this reason, God's Names, in all of their forms, are treated with enormous respect and reverence in Judaism.
The most important of God's Names is the four-letter Name represented by the
Hebrew letters Yod-Hei-Vav-Hei (YHVH). It is often referred to as the Ineffable Name, the Unutterable Name or the Distinctive Name. Linguistically, it is related to the
Hebrew root Hei-Yod-Hei (to be), and reflects the fact that God's existence is eternal. In scripture, this Name is used when discussing God's relation with human beings, and when emphasizing his qualities of lovingkindness and mercy. It is frequently shortened to Yah (Yod-Hei), Yahu or Yeho (Yod-Hei-Vav), especially when used in combination with names or phrases, as in Yehoshua (Joshua, meaning "the Lord is my Salvation"), Eliyahu (Elijah, meaning "my God is the Lord"), and Halleluyah ("praise the Lord").
Jews do not casually write any Name of God. This practice does not come from the commandment not to take the Lord's Name in vain, as many suppose. In Jewish thought, that commandment refers solely to oath-taking, and is a prohibition against swearing by God's Name falsely or frivolously (the word normally translated as "in vain" literally means "for falsehood"). Judaism does not prohibit writing the Name of God per se; it prohibits only erasing or defacing a Name of God. However, observant Jews avoid writing any Name of God casually because of the risk that the written Name might later be defaced, obliterated or destroyed accidentally or by one who does not know better.