“So, you either believe this or you make God out a liar.”
You don’t see the problem do you? If you actually think about it someone can believe in Jesus but “snatch them[selves] out of” Jesus’ hand. You are creating a false dichotomy. It is not:”either [you] believe this or you make God out [to be] a liar.” I believe everything in that verse. Every word of it. I also believe that we can lose our salvation by our own actions separating ourselves from God.
Well, to me the text indicates an outside agent snatching someone out of God’s hand. Can’t be done. If you can “snatch” yourself out (and there is sufficient Biblical evidence that you can do so), then you’re right; but no one else can do it to you and that, I believe, was the sense of the passage.