1. Nothing can separate you from the love of God, which is in Christ Jesus your Lord.
For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come, Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord. (Romans 8:38-39)
Neither death nor anything that happens after death, or anything that happens while you're living can separate you from God's love. If there were no other verse in the Bible that deals with eternal security, this one covers the base.
2. When you are saved, you are made perfect forever.
For by one offering He [Jesus] hath perfected for ever them that are sanctified. (Hebrews 10:14)
When Jesus died on the cross, He saved you forever. Jesus offered one sacrifice for sin forever. If you ever lost your salvation, in order for you to be saved again, Jesus would have to die again. By one offering He has perfected forever those who were sanctified.
3. Our Lord always finishes what He begins.
Being confident of this very thing, that He [God] which hath begun a good work in you will perform it until the day of Jesus Christ. (Philippians 1:6)
Let me tell you what the Holy Spirit of God does for your salvation. First, He convicted you of sin. Second, He converted you. And the Convictor and the Converter is also the Completer. If God fails to finish what He's begun God has failed and He cannot fail.
4. You are predestined to be like Jesus.
For whom He [God] did foreknow, He also did predestinate to be conformed to the image of His Son, that He might be the firstborn among many brethren. (Romans 8:29)
God saw you before this world was put in space. He saw you repent of your sin and ask Jesus to save you. And when God saw that, not only did He foreknow it, but also He predestinated it. If it is settled in eternity how can it be undone in time?
5. You are in Christ.
Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new. (2 Corinthians 5:17)
You are in Christ just like Noah was in the ark. The ark was a picture of Jesus and when Noah went into that ark God shut the door. Noah may have fallen down a lot of times in that ark, but he never fell out of it. Your security is not in a place, it is in a Person and His name is Jesus. And if you're in Jesus, you're secure and if you're not in Jesus you're not secure.
6. You already have eternal life.
Heareth My word, and believeth on him that sent Me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life. (John 5:24)
Everlasting life is not something you get when you die. Everlasting life is something you get when you receive Jesus. If I have everlasting life, when can it end? Suppose I had it 10 years and it ended. Did I have everlasting life? No, I had a 10-year life. Whatever you have, if you ever lose it, whatever it was it wasn't everlasting.
7. The Lord Jesus Christ is ever interceding for you.
I pray for them: I pray not for the world, but for them which thou hast given Me; for they are Thine. (John 17:9)
Jesus also prayed: "I pray not that thou shouldest take them out of the world, but that thou shouldest keep them from the evil...Neither pray I for these alone, but for them also which shall believe on me through their word" (John 17:15,20). Say your name in that verse because Jesus prayed for you! Has Jesus ever prayed a prayer that wasn't answered? No, not one (see John 11:42 and Hebrews 7:25).
Some people say, "Well, if I believed in this doctrine, then I'd get saved and I'd sin all I want to." Friend, I sin all I want to. I sin more than I want to. I don't want to! When you get saved you get your wanter fixed. As a matter of fact, you get a brand new wanter.