The verse was written by King David in reference to himself. When Samuel the Prophet was sent to Jesse's house to choose a king from among his sons (I Samuel 16:1-13), Jesse brought all his sons before Samuel except for David, the youngest, who was in the fields tending the sheep. Samuel thought that G-d would choose the oldest son, but G-d told him, No, I have rejected these. Finally Samuel asked, Do you have any other sons? And Jesse sent for David. G-d said, Arise and anoint him, for he is the one. David was thus the stone rejected by the builders Jesse and Samuel, and he became the cornerstone of the great dynasty of Jewish kings.