How do we know that believers cannot lose their salvation?

The assurance that believers cannot lose their salvation is rooted in the doctrine of the perseverance and preservation of the saints. As noted in 1 John 2:19, those who abandon the faith demonstrate that they were never truly part of the group of believers: 'They went out from us, but they were not of us.' True believers, however, possess the unction from the Holy One, which is the life-giving work of the Spirit that empowers them to remain in Christ. Ultimately, the sustaining grace of God ensures that those who are genuinely in Christ will endure to the end, in accordance with His divine promises.