“four spirits of heaven.” The word “spirits” is ruach (#07308), and ruach has many definitions, including “wind,” “breath,” “spirit” in the sense of the spirit life of a person or animal (Ecc. 3:21), and also “spirit” in the sense of an angel or demon. When great movements of people occur, there is spiritual power and influence involved. Merrill Unger writes: “However, in the realm of human government the unseen personalities of the evil supernatural sphere are just as real and active as their visible human agents, and any deeper interpretation of human history, tracing in it a divine purpose and goal, must take into account the invisible yet very real realm of spirit” (Biblical Demonology, p. 181).
“were stirring up.” The Aramaic can also be translated “broke forth upon” (cp. CJB; JPS). Both meanings have validity, because the great sea is people, and when spirits (angels or demons) move masses of people they move quickly and powerfully, but then keep stirring the people up to action.
“Great Sea.” The common Old Testament name for the Mediterranean Sea. That the term “great sea” is a hypocatastasis and can be representative of many nations, which is the case here in Daniel, is made clear in Revelation 17:15. However, it is most likely the case that in this vision Daniel actually saw a vision of a Great Sea, the Mediterranean Sea, and not a sea of people. But he would have understood the prophetic vision and how the sea is used in biblical prophecy and that it was representing a great mass of people. Daniel would certainly have understood that, as is clear from reading the book of Daniel. [For more information on “great sea,” see commentary on Revelation 17:15, “Peoples, and multitudes, and nations.” For more information on hypocatastasis, see commentary on Revelation 20:2].