I think this song is so cute. It's a metaphor, representing how opposites attract. But without the day, there wouldn't be the night and vice versa. It's saying how opposites depend on each other to help but it's also representing a specific relationship. It's how the girl is all bubbly and golden and the guy is basically a train wreck. She easily picks him up and they fall in love and "all was golden in the sky." I also kind of thought when Brandon said it was in summer, that the longest day of the year is in the summer. Hence, the night is shorter. The sun saved the moon after the longest day of the year by giving it gradually more time to shine. They made a promise to rely on each other so the other doesn't get lonely or down.