God is the one who leads us out of darkness (2:257)

2:257 GOD is Lord of those who believe; He leads them out of darkness into the light. As for those who disbelieve, their lords are their idols; they lead them out of the light into darkness – these will be the dwellers of Hell; they abide in it forever.

One can be a beliver and still be in darkness. It is out of God’s mercy that he sends a messenger to recite God’s revelations to us clearly to lead those who believe and work righteousness out of the darkness into the light.

65:11 a messenger who recites to you GOD’s revelations, clearly, to lead those who believe and work righteousness out of the darkness into the light. Anyone who believes in GOD and leads a righteous life, He will admit him into gardens with flowing streams; they abide therein forever. GOD will generously reward him.