He was not propitiated for the ancient giants: The reference here is to Gen 6.4. He was not propitiated means that his anger never cooled. “He did not forgive” (Good News Translation) and “the Lord refused to forgive” (Contemporary English Version) are good equivalents. Ancient means “lived long ago.” Giants in some languages will be expressed as “huge and powerful men” or “very tall powerful men.”

Who revolted in their might: In their might is rendered “confident of their own strength” by Good News Translation. Confidence is clearly implied here; the giants would not have rebelled if they had not been confident.

An alternative model for this verse is:

• Long ago, when those powerful and confident giants rebelled against the Lord, he refused to forgive them.

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.