Zechariah 6:5
And the angel answered and said unto me, These are the four spirits of the heavens, which go forth from standing before the Lord of all the earth. And the angel answered and said unto me, These are the four spirits of the heavens, which go forth from standing before the Lord of all the earth.
The four are spirits belonging to heaven itself, standing in attendance before the Lord who rules the whole earth. From that place of standing before Him they are sent forth outward into service. Their going forth shows that His eyes remain open over every part of the work. Nothing in His entire cause is hidden from His watchful oversight.