en_tn/zec/13/01.md

a spring will be opened ... for their sin and impurity

Forgiving the people's sins is spoken of as if a spring of water will wash away their sins. This can be stated in active form. AT: "it will be like a spring opens ... to cleanse their sin and impurity" (See: rc://en/ta/man/translate/figs-metaphor and rc://en/ta/man/translate/figs-activepassive)

a spring

a place where water flows naturally out of the ground

the house of David

Here "house" represents descendants. AT: "the descendants of David" (See: rc://en/ta/man/translate/figs-metonymy)