Also, can a believer cease to believe ? That is, can he lose his faith in God ? And if he can, does he thereby lose his salvation ?
I don't honestly know.
I tend to believe that, ... once saved, ... belief is a part of your makeup. Therefore, you couldn't "not believe" any more than you could "not think".
However, ... the writer of Hebrews tells us that ... " ... if it were possible that believers could lose their faith ... that they could not regain it ... ".Hebrews 6:4 For it is impossible ... for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,
5 And have tasted the good word of God, and the powers of the world to come,
6 If they shall fall away, ... to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.