Why Differences in Exodus and Samuel in Dead Sea Scrolls?

You pose a rather broad question. We’ll look at a particular case. For example, in 1 Samuel 17:4, most modern Bibles rely on traditional biblical manuscripts and thus list Goliath’s height as six cubits and a span, meaning a formidable 9’ 9”! In contrast, the Dead Sea Scrolls version of the same lists Goliath as four cubits and a span (6’ 9”).

An article by the Associated Press, published in the year 2000, asserts that the “official” Catholic Bible goes with the shorter height for Goliath. However, the New American Bible (NAB), which is used for readings at Mass, and the Revised Stand Version Catholic Edition (RSVCE), which is used for the scriptural translations in the Catechism of the Catholic Church (CCC), both list the taller height for Goliath, while the NAB acknowledges the alternative view in a footnote.

Some scholars argue that two parallel versions of the Old Testament existed simultaneously in ancient times. Others would argue that Dead Sea Scrolls have deviated from the original text in some respects. Bottom line, the Catholic Church affirms that we can have confidence in the official translations that have been handed down to us.