Good News Translation and New English Bible place this verse in quotation marks to indicate that it is indeed a quotation, or at least a rough one, from words of David in 2 Sam 24.14.

Let us fall into the hands of the Lord, but not into the hands of men: Instead of Let us fall into the hands of the Lord, the Greek reads “We shall fall into the hands of the Lord,” as the Revised Standard Version footnote indicates. Revised Standard Version, and most others, take the clause as it occurs in 2 Sam 24.14. The Handbook suggests that translators stay with the Greek text. Good News Translation does this successfully by interpreting the future tense as an indication of will rather than as a prediction: “We place our destiny in the hands of the Lord.” The hands of the Lord is an idiomatic way of referring to God’s will and activity. Good News Translation is saying “We trust our destiny [or, future] to the Lord.” But not into the hands of men is the opposite: “We are not trusting our destiny [or, future] to human beings.” So we may translate these two lines as “We let the Lord, not humans, decide our future.”

For as his majesty is, so also is his mercy: We are to fear God—honor and revere him—because he is of tremendous majesty, immense greatness. But we may confidently entrust ourselves to him because he is just as merciful as he is majestic. David uttered these words because he had done wrong, and was submitting to God’s punishment. Ben Sira uses the quotation to bolster the courage of someone who may have to face difficult times. Good News Translation‘s model is a good one, but we may also translate these two lines as “because he is just as merciful as he is great [or, powerful/majestic].”

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on Sirach. (UBS Helps for Translators). New York: UBS, 2008. For this and other handbooks for translators see here.