I remember when I was younger I was in constant fear that I might just do something that would "un-save" me. Like I could be regenerate one day and dead in my sins the next. It was no way to truly live. I was living like I had to constantly make religious sacrifices, neglecting the truth that Jesus already paid the price for my sin. I didn't understand what it meant that I had Jesus as a great High Priest pleading with the Father on my behalf. What better assurance for the church, than the fact that Jesus sits as the eternal High Priest?
We live under a new and better covenant, not the old covenant. When Jesus offered the cup at the last supper he said, "This cup is the new covenant in my blood." We don't need the blood of goats and calves anymore. Hebrews 9:11-12 says, "But when Christ appeared as a high priest of the good things that have come, then through the greater and more perfect tent (not made with hands that is, not of this creation) he entered once for all into this holy places, not by means of the blood of goats and calves but by means of his own blood, thus securing and eternal redemption."
The sacrifice of Christ... His blood covering over our sin... Secures an eternal redemption. I am so grateful that my redemption in Christ is secure. He has secured it! I don't have to work for it or earn it! It's all grace. I am thankful that God moved an unknown author to write the book of Hebrews to give us this beautiful assurance! Praise God!