To me, this shows the importance of overcoming the fears and attachments that hold us back from following the path wholeheartedly. Maybe we need to open our ears to our own guardian yakkha-spirits who are encouraging us to pursue through our darkest moments. I still to this day, at 29 years old, notice fear and anxiety arise in me when I am alone in the dark, and most often I retreat into slumber, which is unfortunate and somewhat ironic.
Light seems to appear for Anathapindika in conjunction with the arising of saddha, faith or conviction. The commentary also relates it to joy. Darkness descends along with "fear, terror & horripilation," and perhaps a lack of conviction, either in his own abilities/strength or in the existence of a Tathagata. If the Vinaya version of the story is correct, and if my understanding of stream-entry is also not mistaken, this would be the last time he was to experience such mental states.
We can all be very happy and joyous for Anathapindika, who it seems is well on his way to full awakening and release.
“I in the present who am a worthy one, rightly self-awakened, am a
teacher of action, a teacher of activity, a teacher of persistence. But the
worthless man Makkhali contradicts even me, (saying,) ‘There is no
action. There is no activity. There is no persistence.’ "
AN 3.138, trans. Ven. Thanissaro