BECAUSE HE HAD DOUBT  THAT; THE  STRENGTH OF THE WORD THAT HELPED HIM   TO GO ON THE WATER WAS A MUCH GREATER THAN THE STRENGTH OF THE WIND.IT IS ALWAYS WRONG TO BE AFRAID BECAUSE HE WHO LET US GO IS A FAITHFUL TO HIS WORD SO WE  DON'T HAVE TO FEAR IF WE HAVE HIS WORD BUT WE NEED TO AFRAID IF WE START ANTIN TO HIS WORD.

Jesuse did it just to show as it is the right thing everybody should have to do it