Mystic Riddle

Alone I walk through this life so quietly
My feet so swift...they make not a sound
Nothing can follow me...not even a shadow keeps its place
I can see all except my own pale face
A sift...a rift in time I tear
The past, present, future...I will always be there
This is my riddle to you my sweet
But do not ask twice for I do not repeat
I do not wish to make you fickle my friend
Unfortunately I am both the Beginging and the End
If an answer you can give me...that is true
Then a truelt wonderous give I give to you
For your life I will not slay
And your lifes blood in your veins will stay