BSA_en_tn/1sa/02/30.md

the house of your ancestor

The word "house" is a metonym for the people who lived in the house. See how you translated this in 1 Samuel 2:27. Alternate translation: "the family of your ancestor" (See: rc://en/ta/man/translate/figs-metonymy)

should walk before me

This is an idiom that means "live in obedience to me." (See: rc://en/ta/man/translate/figs-idiom)

Far be it from me to do this

"I will certainly not allow your family to serve me forever"

those who despise me will be lightly esteemed

The words "lightly esteemed" is an ironic euphemism for "greatly despised." This can be stated in active form. Alternate translation: "I will lightly esteem those who despise me" or "I will greatly despise those who despise me" (See: rc://en/ta/man/translate/figs-irony and rc://en/ta/man/translate/figs-euphemism and rc://en/ta/man/translate/figs-activepassive)