Here the words "we" and "us" refer to all believers, including the people to whom John was writing. Unless otherwise stated, that is the meaning for the remainder of this book. (See: [[rc://en/ta/man/translate/figs-inclusive]])
This means that God is perfectly pure and holy. Cultures that associate goodness with light may be able to keep the idea of light without explaining the metaphor. AT: "God is purely righteous like pure light" (See: [[rc://en/ta/man/translate/figs-metonymy]])
This means that God never sins and is not evil in any way. Cultures that associate evil with darkness may be able to keep the idea of darkness without explaining the metaphor. AT: "in him there is no darkness of sin" (See: [[rc://en/ta/man/translate/figs-metaphor]])