Salvation doesn't have an "on-off" switch! Like you do something bad and the Holy Spirit leaves you until you've sought forgiveness. Yes, unrepented sin does distance you from God until he hears your sorrow at what you've done and your genuine intention not to make the same mistake again. But if your life ends before you can do this, your once-for-all profession of faith gaurantees your salvation.
Once Saved - The Gift of Salvation is Eternal
The Bible teaches us that Jesus Christ is our salvation and that it is found in no one else but Him. “Salvation is found in no one else, for there is no other name under heaven given to mankind by which we must be saved” (Acts 4:12).
This one act of Jesus, through His death and resurrection, has provided us the privilege of salvation. We are reminded in John 14:6 that Jesus is our way to the Father which means that His act of saving us is the only way for us to be saved.
Jesus answered, “I am the way and the truth and the life. No one comes to the Father except through me.”
This is a very important fact in our Christian lives. Once we accept Christ, we are destined to always have Him at our side. In Romans 10:9-10, we are reminded by this,
That if you confess with your mouth, “Jesus is Lord,” and believe in your heart that God raised him from the dead, you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved.
This Bible verse reminds us that if we continue to believe, then we are saved. This is further emphasized in Titus 3:5 stating that “He saved us, not because of righteous things we had done, but because of his mercy. He saved us through the washing of rebirth and renewal by the Holy Spirit.”
This scripture also reminds us why Jesus saved us in the first place. It is His mercy that saves us and that we accept His salvation by accepting Him through the gift of baptism of water and the Holy Spirit.
God loves us so much that He gave His only son, Jesus. And therefore, Jesus is our salvation. We are reminded by this in John 3:16-18,
For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. For God did not send his Son into the world to condemn the world, but to save the world through him. Whoever believes in him is not condemned, but whoever does not believe stands condemned already because they have not believed in the name of God’s one and only Son.
These passages point out that once we accept Jesus, we are ultimately saved. It is eternal. But this gift of salvation is not a gift to be taken lightly.
This gift means we are bound to do what Jesus would do, veering away from sin, because the life of a Christian is a never-ending journey to be faithful to Christ.
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Here are some more verses on the certainty of salvation...
Ephesians 2:8-9
For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast.
Because, if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved.
He saved us, not because of works done by us in righteousness, but according to his own mercy, by the washing of regeneration and renewal of the Holy Spirit,
And there is salvation in no one else, for there is no other name under heaven given among men by which we must be saved.”
Jesus said to him, “I am the way, and the truth, and the life. No one comes to the Father except through me.
For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,
Read more on Open Bible.