Even before Jacob heard the angels' report, he knew that Esau was accompanied by 400 men. Yet he was not afraid, since he assumed they were the embodiments of "the 400 worlds of spiritual delight":
Spiritually, the 400 coins that Abraham gave to Ephron (in payment for the Cave of Machpelah35) correspond to the 400 "worlds of delight" that the righteous will inherit in the World to Come. Abraham invested these lofty energies in Ephron in order to extract them later on, much like sowing a field with a small number of seeds in order to reap abundant produce later on. While they remain in the realm of Ephron, however, they take on a negative manifestation.
Jacob thought that the energies of the 400 coins had already been returned to their original holy state and were now embodied in Esau's men. Sadly, the angels reported, Esau's 400 men were the devolved manifestation of these lofty spiritual energies, which had not yet been returned to holiness