Why do people say R.I.P?

I know it is difficult to think of what to say when someone dies, and to appear, at least respectful, butt what does it mean and why say?

Many of the countless synonyms for dying are euphemisms—verbal tranquilizers to help us avoid dealing head on with harsh realities.



When I die ... or kick the bucket, fall off the perch, push up daisies, guess who's not going to shop at Wal-Mart anymore, like dinner guests who take a pass on dessert, no longer with us, "lost" or "asleep.", "called home"  "bit the dust." And to most of us,  "taking a dirt nap." .
OR
Passed, passed on, or passed away

Resting in peace, eternal rest, asleep

Demise

Deceased

Departed, gone, lost, slipped away

Lost her battle, lost her life, succumbed

Gave up the ghost
Didn't make it

Breathed her last

Went to be with the Lord, Went to Heaven, Met his Maker

Was called home, is in a better place

or worse www.you-can-be-funny.com/Euphemisms-For-Death.html

I am basically just going to die and be dead.