In the beginning
The first word in the Bible is the preposition בְּ (B´) which is translated "in". According to a standard lexicon, the basic meaning is "local and instrumental, in, at." However, context determines both the vocalization (vowel) and meaning. With persons, this can be with or among. It can also mean according to, because of or by means of. The phrase בְּרֵאשִׁ֖ית appears here and four times in the historical record of Jeremiah. In those cases, some translations have "at the beginning."
Re´shiyth (רֵאשִׁ֖ית) is a demonstrative form of רֹאשׁ (rosh) and means, "head, chief or first." With no definite article, the phrase might be translated conversationally as "At first" or simply "First".
Having said this, it is significant that Jeremiah's scribe uses the phrase in connection with the reign of the king. This reminds us that the Bible records the sovereign rule of the LORD from start to finish. Everything, within and outside of the Bible, is part of God's plan. He is in control.