The salvation of believers is not secured by their perseverance. They persevere because their salvation is secured by the power of God’s indwelling Spirit.
The elect will never be separated from God’s love in Christ. Nothing presently in this life, prospectively in death, or eternally in the future can sever a true believer from his relationship to God:Who shall separate us from the love of Christ? Shall tribulation, or distress, or persecution, or famine, or nakedness, or danger, or sword? As it is written, “For your sake we are being killed all the day long; we are regarded as sheep to be slaughtered.” No, in all these things we are more than conquerors through him who loved us. For I am sure that neither death nor life, nor angels nor rulers, nor things present nor things to come, nor powers, nor height nor depth, nor anything else in all creation, will be able to separate us from the love of God in Christ Jesus our Lord. —Romans 8:35–39
All the elect will be kept secure by God, even in the face of mounting persecution and even martyrdom. Such painful ordeals will be only the means by which they enter into glory. But Christ will never remove His saving love from them. MacArthur writes, “Only the true believer perseveres, not because he is strong in himself but because he has the power of God’s indwelling Spirit. His perseverance does not keep his salvation safe but proves that his salvation is safe. Those who fail to persevere not only demonstrate their lack of courage but, much more important, their lack of genuine faith. God will keep and protect even the most fearful person who truly belongs to Him. On the other hand, even the bravest of those who are merely professing Christians will invariably fall away when the cost of being identified with Christ becomes too great. Only true Christians are overcomers because only true Christians have the divine help of Christ’s own Spirit.”
—Steve Lawson, Foundations of Grace (Reformation Trust, 2006), 371.