Why is embryonic stem cells used in the treatment of physiological diseases

Embryonic stem cells have the ability to become all types of cells.
That means that those stem cells can become kidney cells, lung cells etc.
If you nurture these stem cells with healty cells from a tissue or an organ, those stem cells will eventually grow into and become the same as the cells you nurtured the with.

This means that you could use embryonic stem cells to create healthy kidneys, skin and other types of tissues/organs.