Why does humanity naturally fear death, especially those who do not profess faith in Christ? It is because we are made in the image of God so eternity is in our hearts and scripture tells us that when we die we face God's judgement against our sin.
And just as it is appointed for man to die once, and after that comes judgment, (Heb 9:27 ESV)
Yet for those who process faith in Christ, there is no fear of judgement as Christ took the judgment for our sin! To be saved means that God has delivered us from his righteous wrathful judgment do us because of our sin against him. It means that we will not be judged for our sins and sentenced to eternal damnation!
For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God. (2Co 5:21 ESV)