The light that was created on the first day, Adam HaRishon was observing in it from the end of the world to its end. We should understand why he says, “from its end to its end,” and not “from the beginning of the world to its end.”
It can be said that when the light shines brightly, the whole world is in equivalence, and there is no beginning or end, but rather the end shines as the beginning. This is similar to saying that he saw the city from afar from the first end to the last end. This is called “from end to end.” But when there is a difference of degrees, we say “beginning and end.”