Romans 8:1 tells us that there is no judgement, no condemnation for those in Christ Jesus. The middle of the chapter tells us why, that God chose us and he predestined us. The end of Romans 8 Paul tells us that that nothing could separate us from the love of God.
Eternal Security: what a wonderful truth of Scripture. I do not need to feel worry or doubt because God has saved me and sealed me. The assurance of salvation is as important to understand as salvation itself. If I could lose my salvation, then what good is the salvation in the first place? Romans 8 tells me very practically, that salvation is through the finished work of the cross, where Jesus Christ took our place.