Here's his idea. Our fear and anxiety are usually some sort of projection into the future on our part. We do what Jesus says not to do (Mathew 6:34) and borrow potential trouble from tomorrow. It's not guaranteed trouble. It's just what we think might happen, and of course we manage to think the worst (whatever it is for you - death, injury, illness, financial ruin, a bad report from the doctor, a plane crash, embarrassing yourself in public, ______________ - supply your particular fear). As Welch notes, "Worriers are visionaries minus the optimism." (p.50) The potential for that future bad thing, then, causes us anxiety or fear.
You see, we're like prophets. We predict the future and then behave in a manner befitting our prophecy. The problem? We usually get it wrong. Rarely are our worst anticipations realized. You know what that makes us? False prophets. The Biblical test of a prophet was, "Did his message come true?". If not, he's not a prophet. Deuteronomy 18:22 "…when a prophet speaks in the name of the LORD, if the word does not come to pass or come true, that is a word that the LORD has not spoken; the prophet has spoken it presumptuously. You need not be afraid of him." Isn't that interesting. You don't need to be afraid of him; or in this case of your own thoughts!
So when you dream up your next dooms day scenario for your life, you know what you can do with it? Ignore it. And even stronger, God also told Israel to put false prophets to death. The parallel here would be putting to death that tendency in your life to pessimistically predict the future; kill your tendency to believe those lies! You've not been right before; why do you give credence to your "prophecy" this time? If we're honest, we don't have a very good track record. Judged by the Bible's standards, we'd be false prophets. Since that's the case, we've quit listening to our false prophecies, right? Well, um, no. So why is it we're still listening?
There's a far better alternative than listening to your false prophecies. Listen to Jesus. His word is always true. He's never been wrong. He has peace and comfort for his people. When you're tempted to believe your own lies, battle them with the truth of his word. As Martin Lloyd-Jones says, don't listen to yourself, talk to yourself. Don't listen to the lies you manage to concoct about the future. Instead speak to yourself the promises of God's Word that you know to be true and that have been repeatedly proven in your life and the lives of God's people for centuries.
This is not to say there will be no bad things in your life. Maybe a few of the bad things you've imagined have happened. Jesus doesn't say there won't be trouble tomorrow, he said there's enough for today, so don't worry about tomorrow. But even when those difficult things come, you know what is true? There will be enough grace. And as my dad has reminded me, that grace for tomorrow's trouble, you'll get tomorrow. Not today.