look at 1 John 5 verses 14-18 ...
this is (not was or will be ) the assurance (promise) that we as christians have ...
that if we ask for anything in His will ( not in his will for us to be defeated, bummed out , and broke) we will have what we say ( speak of victory, not problem)
and if we are not guilty of any unrepented mortal sin, we will have what we say ( devil's kind of hard hearing, so have to remind him like a 2 year old...) and the devil cannot touch you ( like the Mc Hammer song ... can't touch this ...)