In the previous verse, James made it clear that temptation to sin always comes from within ourselves. It’s never God’s fault. No matter how terrible our circumstances are, the desire to sin is still ours. We are tempting ourselves to sin. God provides trials and ordeals as a way to “exercise” our faith, in order to make it stronger. The lure of giving up, sinning, and defying God is not the purpose of His will.
Here James warns us of the consequence of giving into our desire, which is falling into sin. When we say “yes” to the desire to do what we want, instead of trusting God and obeying Him, sin is born. Then sin grows up and produces death.
Sin always leads to death. For those who are not in Christ—who have not accepted God’s free gift of forgiveness of sin, who have not been born again to a new life—that death is permanent and eternal. But even for Christians, sin brings deadly consequences. Later in this letter James will write that when Christians succeed in turning each other back from sin, they save each other from death (James 5:19–20).
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“James 1:15” Bibleref.com
15 Then the lust, when it has conceived, bears sin. The sin, when it is full grown, produces death.