From a letter to one who had fallen into extreme debt, could find no way out, and had become depressed (paraphrased for clarity):
When spirits are down, your confidence in G‑d is weakened. That’s not good, because everything depends upon that spirit of confidence.
Your confidence when things get rough is the measure of how tightly you have tied your material world in with your Creator.
Tighten that rope, ramp your confidence in G‑d up to its fullest, and you will not lack anything—because your world will be synchronized with a higher world where nothing could possibly be lacking.
How do you tighten it? Only by working on yourself when challenges such as these come along.
Real confidence means that even when all natural means have been exhausted, you are perfectly confident, beyond any doubt, that everything is going to be 100% good, visibly and obvious to all—a good livelihood, good health, everything. For G‑d, the natural order poses no obstacle.
As soon as you will raise yourself just a little higher than the earth—as soon as you will get yourself to be a believing Jew, absolutely confident that you have no master over you other than G‑d—then you will be able to make His reality your reality as well.
For you, here in this world, nothing within the natural order will be able to affect you in any way other than for the good.
