“Just as a royal frontier fortress has a gatekeeper, wise, experienced, intelligent to keep out those he doesn’t know and to let in those he does know, for the protection of those within and to ward off those without, in the same way a disciple of the noble ones is mindful, endowed with excellent proficiency in mindfulness, remembering and recollecting what was done and said a long time ago. With mindfulness as his gatekeeper, the disciple of the noble ones abandons what is unskillful, develops what is skillful, abandons what is blameworthy, develops what is blameless, and looks after himself with purity.”

AN 7:63