Hello Boudi,
But if we are still bound to the law then Christ's death and resurrection was for nothing. Then we have to ignore all the prophecies of the Old Testament regarding the coming Messiah.

So you are saying we are no longer bound by laws?  I can commit any act, because I am not bound by laws?  Also, it m,eans that God gave laws for the time being, rather than for all time>  Is this what you are saying?
The prophesies are interpreted according to need as well.  One of the line of David, though this line was through Joseph etc.  To believe these prophesies you have to believe that Joseph was the father of Jesus ( when he probably was).