Why in Chinese Bible (和合本), "you" was translated as "你" instead of "您"?

Because You here is for single not for plural.

• "I thought 您 is more polite and honorific and thus should be used when address Jehovah. Why was "you" translated as "你" instead of "您"?"

你 is, in fact, the correct translation, not only linguistically; but theologically as well. Because God is Father, the familiar form of the second person is appropriate.

A little diversion on the English terms, "thou" is the singular form in Early Modern English, and "you" the plural. The plural form came to be used as a polite form of address later, and "thou" the singular and familiar form. Over time, "you" took over and now Modern English uses "you" as both singular and plural and that distinction between formal (polite) and informal (familiar) is lost.

The translation of the Bible into English has maintained the difference between formal and informal; and it is also correct to maintain the same when translating into Chinese, "Thou/ thee" (informal and familiar) as "你" and "thy" as "你的". It is linguistically faithful. Theologically it is also the correct form since we are talking about a father-child relationship, and it is definitely not formal.

In my opinion, this question is not specific in Chinese. In fact, many languages use the singular form of the second person to address God.

Here is a quote from Wikipedia's article "thou".

Early English translations of the Bible used the familiar singular form of the second person, which mirrors common usage trends in other languages. The familiar and singular form is used when speaking to God in French (in Protestantism both in past and present, in Catholicism since the post-Vatican II reforms), German, Spanish, Italian, Portuguese, Scottish Gaelic and many others (all of which maintain the use of an "informal" singular form of the second person in modern speech). In addition, the translators of the King James Version of the Bible attempted to maintain the distinction found in Biblical Hebrew, Aramaic and Koine Greek between singular and plural second-person pronouns and verb forms, so they used thou, thee, thy, and thine for singular, and ye, you, your, and yours for plural.

From: Baidu: 您

“您”字并非属于通语字，这字原本为地方方言字-- The character “您” was not a standard character, it was originally a local dialect word

~

适用范围: -- Scope of application:

最初的方言字随普通话、通用书面传播到全国。-- The original dialect word spread throughout the country with Mandarin became standard writing.

官话：(Mandarin)

你，第二人称词。(second-person pronoun)

您，第二人称词，敬称。(second-person pronoun, honorific)

南方语言（譬如：客家语、粤语、闽南语等）：(Southern dialects (for example: Hakka, Cantonese, Hokkien, etc.):

你，第二人称词。 (second-person pronoun)

From: WiKi: Bible translations into Chinese

The first translations may have been made as early as the 7th century AD, but the first printed translations appeared only in the nineteenth century

The Chinese Union Version is the predominant translation of the Bible into Chinese used by Chinese Protestants, first published in 1919.

From the research above:

您 was not used in Southern dialects before Mandarin education was pushed through the nation.

The Chinese Bible Union Version was published in 1919, predated the national standardization of Mandarin education. Therefore, 你 was still the only second-person pronoun in southern China. Since Christianity reached southern China before spreading to the north, it is reasonable to believe that the early Bible would use the local dialect 你 instead of the Mandarin 您

One more note: I have never seen 您 was used instead of 你 in any Hong Kong publication when I was young.

您 is polite. However, it doesn't necessarily mean 你 is impolite.

你 is more factual and can be used universally for you.

People use 您 as a compliment, e.g. 麻烦您了.

In the OP's context, I think both are fine. 您 probably shows more respect to that person as indicated by OP.

“您”属于北方方言，在普通话推广前并不通用。 “您” belongs to the northern dialects, it is not used by a lot of areas in China before Mandarin education becomes mandatory. Bible wants to reach the majority of people, thus the more generic “你” is used.