S.Baring-Gould

Thus the saying of David, “Thou hast heard me from among the horns of the unicorns,” which signified that David was assisted by God in trouble, was taken quite literally by the Rabbis, and a story was invented to explain it.

In the beginning, before the creation of heaven and earth, God made the angels; free intelligences and free wills; out of His love He made them, that they might be eternally happy.

And that their happiness might be complete, He gave them the perfection of a created nature; that is, He gave them freedom.