God is the absolute master of all reality, responsible for the full spectrum of existence, from the rise of empires to their ultimate fall. While the world appears to be driven by opposing forces, they all flow from a single divine source. The primary approach among commentators is that highlighting these extreme opposites is meant to reject the popular Persian belief in two separate powers, a god of good and a god of evil. By declaring control over both ends of the spectrum, God clarifies that He alone commands all forces [רד״ק בשם רב סעדיה גאון]. However, a different perspective questions why a message meant to praise the Persian King Cyrus would directly attack his religion, suggesting that perhaps Cyrus himself did not actually hold this dualistic belief [שד״ל].
On a historical level, these opposing forces refer directly to the events of that era. God brings light and peace to Israel and the righteous. At the exact same time, He decrees darkness and disaster—meaning war and destruction—upon the Babylonian empire. This dramatic shift of power is part of His broader plan to strengthen Cyrus [רש״י, מצודת דוד, אבן עזרא].
There is a profound difference in how God brings these opposing states into existence. Because light is a tangible entity with actual properties, God shapes and gives it form, designing something that already exists. Darkness, however, is not a physical thing but merely the absence of light, such as when the earth blocks the sun. Therefore, God simply decrees its existence, bringing it forth from nothing [אבן עזרא, רד״ק, מלבי״ם].
A similar dynamic exists between peace and evil. Peace represents a positive, active state of wholeness and harmony. It is the connection of all the different parts of creation working together smoothly, much like a healthy, balanced body. Evil is the exact opposite. It represents war or physical illness, which occurs when there is a clash or a loss of balance in nature. God decrees the underlying possibility for this evil to exist, even though humans often bring illness or ruin upon themselves through their own choices [אבן עזרא, רד״ק, מלבי״ם].
Looking deeper, the existence of darkness and evil is an unavoidable result of creating a physical, ever-changing world. God did not create evil as an independent goal. Instead, He designed a reality that includes lack and absence, because only against that backdrop can goodness truly be revealed. Every single component, whether positive or negative, is absolutely necessary to build and complete the structure of creation just as His wisdom planned [מלבי״ם, שטיינזלץ].