be grateful to sb and seek ways to return his kindness;/救命之恩不敢忘，定将～，以报大德。I can never forget you’ve saved my life. I’m very grateful and will seek ways to repay your great kindness.
结草衔环jie cao xian huan
show gratitude even after one’s death
结草衔环jié cǎo xián huán
结草：把草结成绳子；衔环：嘴里衔着玉环。表示感恩报德之心终身不忘。express gratitude to one’s benefactor, be grateful to sb. and seek ways to return his kindness