en_tn_condensed/zec/12/10.md

I will pour out a spirit of compassion and pleading on the house of David and the inhabitants of Jerusalem

Causing the people to be compassionate and to plead is spoken of as if the spirit were a liquid that Yahweh would pour on them. Alternate translation: "I will cause the house of David and inhabitants of Jerusalem to have mercy on others and to pray to me for mercy" (See: rc://en/ta/man/translate/figs-metaphor)

a spirit of compassion and pleading

Here this means to have a characteristic of compassion and pleading.

the house of David

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

the one they have pierced

"the one whom they stabbed to death"

for an only son

It is understood that the "son" has died. Alternate translation: "for an only son who has died" (See: rc://en/ta/man/translate/figs-ellipsis)