draw a line in the sand

verb3

1. •
   To lay down a challenge; to provide a test of commitment (often one which carries a high risk) to a cause.

   • And Jesus draws a line in the sand and says,' He that is without sin among you, let him cast the first stone." — 2008
2. •
   To indicate the threshold or level above which something will become unacceptable or will provoke a response; to create a boundary and imply or declare that its crossing will provoke a (negative) response.

   • “A line has been drawn in the sand” against any Iraqi invasion of Saudi Arabia, Mr. Bush said. — 1990
3. •
   To create a real or artificial boundary or distinction between (two places, people or things).

   • At some point you ask, "Where do we draw a line in the sand between deconstruction as desertification of God and as desertion of God?" There is no line. — 1999