Jesus is the true Light who gives light. Light here is used in a metaphorical sense for understanding. Just as the light of a lamp allows us to find our way in the dark, so God has given us the ability to understand things. The expression, “now I see the light!” means, “now I understand!” Jesus, the true Light, gives this ability to all men.
But why is John making this point?
Jesus came into this world “to His own [place] and His own [people]” in fulfilment of prophecy.
"But you, Bethlehem Ephrathah,
Though you are little among the thousands of Judah,
Yet out of you shall come forth to Me
The One to be Ruler in Israel,
Whose goings forth are from of old,
The nation of Israel knew of this prophecy and many others like it. They had been waiting for their “Ruler” for hundreds of years! Jesus came in fulfilment of these prophecies and even highlighted Bible passages in reference to Himself (Luke 4:21), but the nation refused to acknowledge Him. They rejected Him and would “not receive Him.” They had the ability to see but refused to accept what was obvious. They could have known Him if they wanted to but they choose darkness.
What about you? Have you acknowledged Jesus? Is it because you cannot see who He is ? or because you don’t want to? You can know what the Bible says about the salvation that is in Jesus alone. God has given the ability to understand.