Albert Barnes on Matthew 10:28

Them which kill the body. That is, men, who have no power to injure the soul, the immortal part. The body is a small matter, in comparison with the soul. Temporal death is a slight thing, compared with eternal death, he directs them, therefore, not to be alarmed at the prospect of temporal death; but to fear God, who can destroy both soul and body for ever. This passage proves that the bodies of the wicked will be raised up to be punished for ever.

In hell. Mt 5:22.

(s) "And fear not" Is 8:12,13, 51:7,12, 1Pet 3:14