In simple words, it is because of respect. The Hebrew name of God is given a great degree of reverence such that it cannot be erased or disrespected in any means once it is written or printed. Actually, this custom derives from an interpretation of the commandments by Moses, found in Deuteronomy 12:3-12:4. In this part, Moses instructs his followers to destroy anything associated with the gods of their rivals and they are not to let this happen to their own God.
Judaism does not prohibit writing the name of God. The prohibition is against destroying it some way. Erasing, tearing, throwing the paper away and all are considered means of tarnishing God’s name. Since anything printed or written is likely to be damaged some point of time, they use the word with extreme care. A convenient way to avoid the chance of disrespect was to refrain from writing the name of God. This applies to the sacred Hebrew names of God, such as YHVH, Hashem and Elohim, found in Torah, the Hebrew Bible.
Even though there is no rule against writing and erasing God in English, many Jews treat the word with same respect as in Hebrew. So when writing, they use ‘G-d’ instead of ‘God’ in case it would be destroyed in future. It is actually a recent custom, and prevents others from destroying the name of God. Since the word is not complete but conveys the idea well, there is no risk of defacing the name. It can be erased or damaged later without disrespecting the God. Some use the word G!d as a mean to express both respect and wonder.
The Jews are even reluctant to say the name of God aloud. Instead they use phrases like ‘the Creator,’ ‘the Merciful One’ and ‘Master of the Universe’ to refer the God. Many Jews wouldn’t discard paper or books which contains God’s name in Hebrew either. Those books are regarded with a great amount of respect and the believers would rather store such documents in a genizah (a storage place in synagogue) and sometimes bury them in a Jewish cemetery.
The evolution of technology has triggered various debates over the writing of God’s name on the computer and other electronic devices. The general agreement is that the rule doesn’t apply to the modern devices. The deletion of God’s name on a computer screen is not considered a violation of the rule.
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