Actually, the translators had no choice. The Old Testament and the New Testament are two entirely separate sets of books. The Old Testament was completed about 400 BC. By 132 BC the entire Hebrew Bible - The Old Testament - was translated into Greek [the Septuagint version]. The New Testament didn't begin to be written until about 40AD and was not completed until the writing of the book of Revelation by John about 100 AD.
The Old Testament dealt with the revelation of God's purpose beginning with Genesis and then through the books about and directed to the people of Israel. The New Testament deals with the extension of salvation to all mankind through the gospel.
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