'Belief' in the Bible

Nevertheless even from among the Rulers many believed in Him. But because of the Pharisees they did not avow their belief, for fear they should be shut out from the synagogue.

Why is it deemed with all of you a thing past belief if God raises the dead to life?

And from us thanks are always due to God on your behalf--brethren whom the Lord loves--because God from the beginning has chosen you for salvation through the Spirit's sanctifying influence and your belief in the truth.