pin David to the wall with the spear

throw his spear so it would go through David and into the wall

he might kill him

"Saul might kill David"

Michal told David

Here "save your life" is an idiom that refers to escape. AT: "If you do not escape" (See: rc://en/ta/man/translate/figs-idiom)

This can be stated in active form. AT: "someone will kill you" (See: rc://en/ta/man/translate/figs-activepassive)