How do we know that believers cannot fall from grace?

The assurance of salvation for true believers is rooted in their being 'kept by the power of God through faith' as stated in 1 Peter 1:5. This indicates that salvation is not maintained by human effort but is a work of God. If someone claims to be a believer but subsequently falls away, it demonstrates that they were never genuinely saved to begin with. This understanding aligns with the doctrine of the perseverance of the saints, which highlights that those whom God has elected, redeemed, and saved will ultimately be preserved to the end. The consistent biblical theme is that nothing can separate true believers from the love of God.