εἰ δὲ τοῖς ἐκείνου γράμμασιν οὐ πιστεύετε, πῶς τοῖς ἐμοῖς ῥήμασι πιστεύσετε;

1. εἰ
   if
2. δὲ
   but
   and
3. τοῖς
   the
   to the
4. ἐκείνου
   that
5. γράμμασιν
   writings
   letters
6. οὐ
   not
7. πιστεύετε
   believe
   you believe
8.  
   ,
    
9. πῶς
   how
10. τοῖς
    the
    to the
11. ἐμοῖς
    my
12. ῥήμασι
    words
13. πιστεύσετε
    you will believe
    will you believe
14.  
    ;
     

But if you do not believe his writings, how will you believe my words?