Good. Now please ask yourself, what happens if you sin to a greater or lesser degree just before death.
Please consider the following cases:
a) You are a great Christian, but you are angry with someone, don't forgive them, and then you are run over by a car.
b) You are a great Christian, but you are angry with someone, and you set fire to their dog, and then you are run over by a car.
c) You are a great Christian, but you are angry with someone, and you murder them, and then, you know, splat.
In each case - what happens? Are the results in each case all exactly the same?
The reality is that in cases a) and b) you would arrive before the beatific vision of God, but the (arguably) minor sins you carried with you would have injured your soul to a greater or lesser extent. God would heal you of the effect of these venial sins, but the process would hurt. (See Luke and Corinthians above).
And in case c) you would have committed a mortal sin right before death. You broke your soul and are now beyond the time of repentance: hell is your likely reward. In such a situation it would be vain to protest that Christ died for you, so your sins somehow don’t matter – you would have rejected God.
Jesus died for that sin as well as any other I may commit. I will go immediately to heaven (assuming the car has killed me).
b) You are a great Christian, but you are angry with someone, and you set fire to their dog, and then you are run over by a car.
Well, I would never do this, but for purposes of argument - again, Jesus died for this sin as well as any others I may commit. I would go immediately to heaven.
c) You are a great Christian, but you are angry with someone, and you murder them, and then, you know, splat.
Same as the answer to b.
In each case - what happens? Are the results in each case all exactly the same?
Yes, because the blood of Jesus is sufficient. He said, "It is finished" or "tetelestai" (meaning the debt is paid - I believe that's spelled correctly). At any rate, I know I could not save myself by doing "stuff" to begin with, so why would I think I can keep myself saved by doing "stuff"?
As Christians we do "stuff", but it is because of the Holy Spirit within us, not because we are trying to do something now that we never had the power to do in the first place.