Where does it say *some*???
Or did you just add that on your own?
And there's nothing implied in the use of *may* other than that this was written so that people are capable of, have the opportunity to, believe; to possess eternal life
Greek is echo: "to have, hold"
Definition: I have, hold, possess.
Short Definition: I have, hold, possess
To say "you may believe" implies the possibility that you may not believe. So, some believe, others don't.