God sent His Son, Jesus, to be our Substitute and Deliverer from condemnation. Jesus, the "Lamb of God", took upon Himself all God's wrath against sin once and for all time. His purpose was "that through death He might destroy him who HAD the power of death, that is the devil, and (Catch this now!) deliver them who through fear of death were all their lifetime subject to bondage" (Heb. 2:14-15). How could you be delivered from the fear of death IF you could lose your salvation? You could never be free of that bondage. But you ARE free, beloved.
If you have received Jesus by faith in His shed blood on your behalf, you are totally forgiven, forever and unconditionally! The Judge Himself, your heavenly Father, has justly declared you righteous, a "new creation in Christ Jesus". Give me the chance to convince you that you cannot lose the gift of God. Jesus is the Guarantee! Enter into that promised rest God promises all who are His. We received salvation by God's grace. We didn't earn it. We don't deserve it. We do not have to struggle to maintain it. No! Jesus, our Good Shepherd, keeps His sheep safe and secure. We are kept, protected, and deeply loved because we are IN Christ. There is no merit involved. It is "by grace through faith"!