The 1st reading (Is 8:23-9:3) and the Gospel (4:12-23) speak that "the people that lived in darkness has seen a great light.”
Light is such an important thing that God created it even before He created heaven and earth. Once light began to exist, many good things followed it. If you look around us, we find that light helps us in many ways.
In contrast to the light is darkness. Night and darkness are times of sleep. Nothing grows in darkness. If it is dark too long, everything dies. We also refer to darkness as a time of sin, the time of evildoing, the time of Satan. We feel uneasy and afraid in times of darkness.
The darkness of Paganism, ignorance of the true nature of God has been expelled forever by the coming of the Son of God as the Light of the World.
"The Lord is our Light and our help" and whoever follows Him will not walk in darkness, but will have the light of life.
Psalms: "Hope in him, hold firm and take heart.
Hope in the Lord!" (Ps 26:24)