Jesus tells us He is the bread of life and that as we believe in Him, so we will live eternally, raised up with and by Him on the last day. He also tells us that as we “follow [Him], [we] will not walk in darkness, but will have the light of life.”
“Come, follow Me,” Jesus says to His disciples. We believe and we follow.
In darkness, it’s hard to see. True, eventually, the eyes adjust and sight is easier. But what is seen is vague and the truth is not easily perceived. In light, all is visible. Everything is clear.
Life is hard enough as it is; why walk through it in the dark?