See Jeremiah 31:31-34 and Luke 22:14-23. This is language first used in Jeremiah's promise of rescue and renewal of the exiled people of God in Babylon. It promises a coming day when God would make a new covenant unlike the one which Israel had broken.
“And when you fast, do not look gloomy like the hypocrites, for they disfigure their faces that their fasting may be seen by others....
Then Isaac called Jacob and blessed him, and charged him, and said to him: “You shall not take a wife from the daughters of...
Brothers, I do not consider that I have made it my own. But one thing I do: forgetting what lies behind and straining forward...
