...You don't have to live in fear of missing heaven.
Philippians 1:6 Being confident of this very thing, that He which hath begun a good work in you will perform it until the day of Jesus Christ.
God keeps His word. He is steadfast, unchanging, dependable, and faithful. When He speaks, it comes to pass. No one has ever made more promises than God. No one has ever kept more promises than God. He is faithful. He doesn't call you because you are the greatest. He calls you because He wants to work in you, and He gets the glory. God has never called anybody to service and left them untrained. Never.
As a born again Christian, you are created in Christ Jesus unto good works. If God has begun a work in you from the inside out, you can be confident that He will perform it to the end. That's security.
The Bible says you must be born again to go to heaven. God's grace keeps you forever because you're His child.
