“Then when desire conceives, it gives birth to sin, and when sin is full grown, it gives birth to death.” James 1:15 NET
James describes from verse 14 onwards that we are personally responsible for our sins. While God might try us, His objective is not to see us fail. We are tempted and fail due to our own lusts – and the inability to control them. When our lusts go too far, when we do not control them they lead to sin. James says this then leads to death.
The Lampstand Magazine and many conservative Christadelphians insist on a reading of Romans 5:12 that replaces the word death with mortality (claiming the words are equivalent). Clearly such an approach is nonsense – the word mortal cannot fit in James 1.
Furthermore the passage simply shows that death can be used as the fate of the wicked. All humans sin but some will never die 1 Cor 15:51. James is not talking about the forgiven saints whose death is elsewhere styled sleep. They do not die because of sin. It is those who allow sin to reign in their mortal bodies who will reap the reward of death. For those saved by grace it is an altogether happier story as Paul says:
“we were dead in transgressions, [but God has] made us alive together with Christ—by grace you are saved.” Eph 2:5 NET