By faith we trust. 
By faith we believe. 
By faith we pray. 
And by faith we receive.

When you have prayed to Him have faith that your prayer is received.  Then watch.  Watch the thoughts of your mind.  Watch the actions of others.  Watch the situation change.  Pay attention to what is small.  Expect a miracle but take what is given.

But if we say, “Nothing has happened.  God did not hear me.”   How is there any faith in that?

There are many reasons why faith is necessary.  But no reason I can think of fulfills the completeness of its necessity.  Simply have faith that faith is necessary.  And when that is done, have faith.

By His Grace