raison d'être

The fundamental reason for something or someone to exist; the sole or most important purpose for someone or something. From French, literally "reason for being." I know it's something of a cliché, but my children really are my raison d'être. We've always prized serious social commentary as our magazine's raison d'être.

his, your, etc. ˌraison ˈd’être

/%reIzQ~ "detr@; American English %reIzoUn/ (from French) the most important reason for somebody’s/something’s existence: Work seems to be her sole raison d’être.

The meaning of the French phrase is ‘reason for being’.