Why say thank you before anything has happened today?
Most thank-yous come after something good happens. This one comes first. You have not eaten, checked your phone, or even stood up.
The Kitzur Shulchan Aruch (a short guide to daily Jewish law from the 1860s) explains what you are thanking for. When you went to sleep, you handed over your soul tired and worn out. In the morning you got it back new and rested. Then he adds: every morning a person becomes a new creation.
So the thank-you is not for something that will happen today. It is for today. Being awake is the gift.
The Midrash goes one step further. Rabbi Alexandri says: because You make us new every single morning, we know You can be trusted for the biggest return of all, bringing the dead back to life. Waking up is the small daily proof.
One more thing. These closing words were first said in Eichah, in the worst of times, with Jerusalem in ruins. Saying them never depended on having a good day ahead.
Kitzur Shulchan Aruch 1:2,Eichah Rabbah 3:8, on Eichah 3:23Faith is something I have. What is God's "faithfulness"?
The Hebrew word is emunah. We usually translate it as "faith," meaning what a person believes. But here it belongs to God: emunatecha, Your emunah.
The root (alef, mem, nun) means firm or steady, something you can lean on. When Moshe held up his hands during the battle with Amalek, the Torah says his hands were emunah, steady, until sunset. It is also the root of amen, which means "that is solid."
So the plain meaning here is that God is reliable. The Mishnah Berurah (a central commentary on daily Jewish law, written around 1900) explains: God keeps His trust by returning, every morning, the souls that were left with Him at night.
You may have heard this line explained another way: "God has great faith in you." He gave you another day because He believes you will do something with it. Many teachers say this, and it is a powerful thought. It is a later reading, not the plain meaning of the verse.
Shemot 17:12,Mishnah Berurah 1:8What does sleeping have to do with dying?
The Gemara says sleep is one-sixtieth of death. In other words, a small taste of it. When you are asleep you are not in charge. You cannot protect yourself, decide anything, or even know that time is passing.
That is why the prayers around sleep talk about handing yourself over. In Adon Olam we say: "Into His hand I entrust my spirit, when I sleep and when I wake." That line is built on a verse in Tehillim: "Into Your hand I entrust my spirit." The Hebrew word for "entrust," afkid, is the word for leaving a deposit with someone.
Modeh Ani is the other half of that sentence. At night: I am leaving this with You. In the morning: You gave it back.
The Midrash follows the idea to its end. If God returns a soul every morning after a small taste of death, that is the reason to trust Him about the real thing.
Berakhot 57b,Tehillim 31:6,Bereishit Rabbah 78:1