Why is it impossible for a true believer to lose their salvation?

It is impossible for a true believer to lose salvation because it is grounded in the unchanging nature of God and the efficacy of Christ's atonement. As stated in Romans 8:30, those whom God justifies, He also glorifies, ensuring their ultimate preservation. Furthermore, Jesus' declaration in John 6:39 confirms that He will lose nothing of all that the Father has given Him. Thus, salvation hinges on God's sovereign power and commitment, affirming that the elect will persevere and be secured forever in Christ, leading to the conclusion that they cannot fall from grace.