Is this a magic spell? If I say God's own words, does God have to forgive me?
The Gemara does say something that sounds like that. Rabbi Yochanan (a leading sage of the 200s) says God told Moshe: whenever Israel sins, let them do this order before Me, and I will forgive them. Rav Yehuda adds that a covenant was made with the thirteen, so they do not return empty. Rashi explains that this is about Israel mentioning them in the prayers of a fast day.
But look at who the words are about. The Gemara reads the doubled Name, "Hashem, Hashem," as God saying: I am the same before a person sins and after he sins and repents. And on the word "clears," Rabbi Elazar says the verse cannot mean only that, because it goes on to say "does not clear." So it means: He clears those who return, and does not clear those who do not.
The prayer itself says it a few lines earlier: "You taught the way of repentance." Put side by side, these sources tie forgiveness to turning back. Still, the promise in the Gemara is stated strongly, and none of these sources spells out what happens if someone says the words without changing. That part stays open.
Moshe's own use of the words was an argument, not a formula. After the spies, he reminded God what God had said, "even for the wicked," and God answered: "I have forgiven, as you said."
One honest wrinkle. In the Torah, "I am making a covenant" (Shemot 34:10) is about wonders God will do for the people. The Maharsha says the plain reading answers Moshe's earlier request that God set Israel apart from all other peoples (Shemot 33:16). He notes that the Gemara reads it as being about the thirteen attributes written just before it. So the promise is a teaching built on the verse, not what the verse says on its face.
Rosh Hashanah 17b,Rashi on Rosh Hashanah 17b,Yoma 86a,Sanhedrin 111b; Bamidbar 14:17-20,Maharsha on Rosh Hashanah 17b; Shemot 33:16 and 34:10The verse goes on: God "does not clear the guilty." Why does the prayer stop before that?
In the Torah the sentence does not end where the prayer ends. After "and clears," it says: "but He does not clear, remembering the wrongdoing of parents on children and grandchildren, to the third and fourth generation." The prayer stops at "and clears" and goes straight to Moshe's reply.
Is that hiding something? Moshe did not hide it. When he quoted the words back to God after the spies, he included "does not clear" and the part about the children (Bamidbar 14:18). God answered, "I have forgiven."
"Clears" and "does not clear" side by side look like a contradiction. In the Gemara, Rabbi Elazar says it cannot mean only "clears," since the verse says "does not clear," and it cannot mean only "does not clear," since the verse says "clears." So: He clears those who return, and does not clear those who do not.
Rashi gives that reading, and also what he calls the plain meaning: God does not let the sin go completely, but collects from the person little by little. On the children, he says it applies when they hold on to their parents' deeds, since another verse adds "of those who hate Me."
The Gemara also finds an order inside the verse. Ilfai, a sage, notes that it says both "truth" and "abundant in kindness," and explains: first truth, and in the end kindness.
Why stop there, then? The Maharal (Rabbi Yehuda Loew of Prague, died 1609) takes this up. He explains the usual practice: a person should not mention "remembering the wrongdoing of parents on children" in a prayer, as if he were asking for it. But he made a different choice himself. Since Moshe said the verse through "the fourth generation" when he prayed after the spies, the Maharal writes that he made it his practice to say it to the end of the verse.
Shemot 34:7-9,Bamidbar 14:18-20,Yoma 86a,Rashi on Shemot 34:7,Rosh Hashanah 17b,Maharal, Netivot Olam, Netiv HaTeshuvah 6These lines are about God. What do they have to do with how I treat people?
The Gemara answers with one word. In the Song at the Sea the Torah says, "This is my God, and I will beautify Him" (Shemot 15:2). Abba Shaul, a sage of the Mishnah's time, says the word for "beautify" means: be like Him. As He is gracious and compassionate, you be gracious and compassionate.
The Rambam (Maimonides, the great Jewish legal scholar and thinker, died 1204) turns this into law. In his code he writes that this is how the sages explained this commandment: as God is called gracious, you be gracious, and as He is called compassionate, you be compassionate. The prophets used names like "slow to anger" and "abundant in kindness" to show that these are good ways, and a person must lead himself by them.
Note his limit: "as much as he is able." He asks for likeness only as far as a person can reach.
Now read the list that way. Rashi explains "slow to anger" as holding back anger and not rushing to punish, in case the person repents. "Abundant in kindness" is for people who need kindness because they do not have enough good deeds to stand on. Those read like descriptions of behavior.
The Moshe story shows it does not come automatically. His first reaction was that patience should be only for the righteous. God told him he would need it for the wicked, and he ended up using it for a people that had sinned.
Shabbat 133b,Rambam, Laws of Human Dispositions 1:6,Rashi on Shemot 34:6,Sanhedrin 111a-111b