There's only one problem with that analogy… but it turns out it's not a problem at all: No skydiver with any sanity jumps out of a plane without his reserve 'chute. And the reason for that is very, very pertinent to this discussion. Ultimately, skydivers do not trust their main chute. If they did, they wouldn't carry a reserve, right? The skydiver has added something to the main 'chute (in this case wisely) and by doing so, reveals his lack of trust in the main 'chute. Again, this is smart… for a skydiver. But with respect to Christ, do we need a "reserve 'chute"? Do we think Christ is likely to fail us in some way? Was His work sufficient or wasn't it? Is it possible that somehow He forgot about one or two of our sins? Should we rely also on our morality and good works as a sort of "reserve chute"? Do we need a "B-plan" for our salvation? Do we need to supplement Christ's work? And if we think we do, then doesn't that mean we don't really trust in Christ?
Is it possible to be saved if you do not trust in or rely on Christ? No, it's not. We are to trust in Him and Him alone… nothing added, no "B-plan". Christ is all that's necessary, He is absolutely trustworthy. Your own works and obedience is the wrong object to place your faith in; they are not capable of saving you.
Paul makes this point very clear in 1 Corinthians 15:13-14 when he says:
"But if there is no resurrection of the dead, not even Christ has been raised; and if Christ has not been raised, then our preaching is vain, your faith also is vain."
In other words, if the things which we believe are not true, then believing them is useless. Our "faith" is only as effective as the thing which we place that faith in. Our faith does not have the ability to change reality… if we believe in things that are false, or put out trust in things that cannot accomplish for us what we want them to accomplish, then we are fools and we are to be pitied.
To say that there's anything you can do to lose your salvation is to say that your salvation depends on more than Christ… it's to say that your salvation depends on you. It suggests that salvation requires Christ plus something, such as your good works or obedience or your "perseverance."
When Christ tells us to trust in Him, He's telling us to jump out of the plane with no reserve. He will save you. Period.
Some folks might understand me to be saying that you should not do good works, you should not be obedient, etc. But this doesn't follow from what I've said. I said not to rely on your good works, your obedience, for your salvation. That's not the same as saying don't do those things. What I'm saying is simply that your obedience and your good works contribute precisely nothing to your status as a born-again Christian.
Here's the string of verses promised earlier:
John 3:15, John 3:16, John 3:18, John 3:36, John 5:24, John 11:25, John 20:31, John 1:12, John 6:29, Mark 16:16, Acts 13:39, Rom 10:9, Rom 3:22, 1Cor 1:21, 1John 5:13, Acts 16:31, Rom 10-9, John 3:18