to remain on the [important] subject of someone or something for a long time. (Upon is formal and less commonly used than on.)I can't dwell upon this subject anymore.There is no need to dwell on Sarah further.
to live on something, such as the planet Earth. (Upon is more formal than on.)This is the largest turtle that dwells upon the earth.Many creatures dwell on this earth.
Also, dwell upon. Linger over; ponder, speak or write at length. For example, Let's not dwell on this topic too long; we have a lot to cover today. [c. 1500]