Matthew 10:28 And fear not them which kill the body, but are not able to kill the soul: but rather fear him which is able to destroy both soul and body in hell. (repeated in Luke 12:4, 5)
Assertion: This shows God will punish people in hell.
God is able to destroy both soul and body in hell! But! There are two resurrections. The "second resurrection" is of all those who have died without having been saved first. Following this raising from the graves of all those not saved, will be the final day of the examination of all things, all human history, etc. commonly called "the Day of Judgment" and at the end of this, finally, is when those notorious words "those not believing will go to the second death" (Revelation 20:15). Yes, I paraphrased that! "All those not written in the Book of Life will be thrown into the Lake of Fire." {Note: "the lake of fire which is the second death" Revelation 20:14}
It seems quite obvious that at the time it is spoken, after all persons have experienced being resurrected and have lived through and witnessed a very long day of the examination of all things, who, after all that, isn't going to believe? If they are that stubborn perhaps there is only one possible outcome and both soul and body of such ones would be "destroyed". But, since God can only be perfect (or He too would fade/not live) the 'end' result of all this (human history, this unavoidable journey and lesson) can only be perfect.
This, is what Jesus meant when He said to some Pharisees and Saducees "if you do not repent you will die in your sins" (John 8:24) that the "first resurrection" far surpasses the "second resurrection" (at first at least) for to be raised in the "second resurrection" is to be raised in your sin, flaws and imperfection, still in that fearful lost state, rather than in the bright joy of the "first resurrection" when "mortal shall put on immortality" 1 Corinthians 15:54.