As a child I was taught that our salvation depends on us making a decision for Christ. On praying a prayer to God, we are guaranteed salvation, no matter how we live for the rest of our lives, we learnt.
As I grew older, I discovered that the Bible teaches that our salvation is God's doing, and is granted on the basis of Jesus' death, not on our good works. I still found people following on from this and saying that therefore it doesn't matter how we live, because our salvation is assured and is not based on our good works but on Jesus' death.
However, I also found the New Testament teaching the necessity of perseverance as well.
How can my persevering be essential, and how can I have assurance of salvation now, if it is necessary for me to persevere in holiness? What if I don't?
John Piper's dear father, recently ushered into the presence of Jesus, shares his perspective on this in the 4 minute video at the above link.