There are two eye spaces here, the left one promising two eyes.
strikes the vital point, preventing Black from making two eyes there.
After securing one eye, destroys the other eye. on a works, too, but leaves an additional ko-threat.
When Black secures the right eye first, destroys the left eye.
There is no chance for forcing a ko, because after , captures two stones.
After , White killing the left eye first is not a good idea, because creates another potential eye.