Who decided there are exactly thirteen things a Jew has to believe?
The Mishnah has no list of thirteen. Sanhedrin 10:1 says that all of Israel has a share in the World to Come, then lists who does not: one who denies that the Torah teaches the dead will live again, one who denies that the Torah is from Heaven, and the apikoros (the Rambam explains: someone who scorns the Torah or its scholars).
The Rambam wrote his Thirteen Principles as a commentary on that Mishnah, and he was strict about them. Someone who believes all thirteen, he writes, belongs to the people of Israel even if he sins badly. Someone for whom one of them breaks down "has left the community."
Not everyone agreed. In the Mishneh Torah, his law code, the Rambam rules that a person who says God has a body is a heretic. The Raavad (Rabbi Avraham ben David of Provence, who wrote sharp notes on that code) objects: "Why does he call this person a heretic? People greater and better than him went with this idea," because of how they read certain verses.
Rabbi Yosef Albo (Spain, around 1425, author of Sefer HaIkkarim, "The Book of Principles") quotes the Raavad's note in a different wording. There the Raavad first agrees that God has no body. His point is that someone who got this wrong honestly, by reading verses literally, should not be called a heretic.
Albo also questions the number. He counts three roots: God exists, the Torah is from Heaven, and God watches and repays what people do. In his view, beliefs like the coming of the Mashiach are true and a Jew must accept them, but they are not roots. His rule: someone who holds on to the Torah, and whose honest study leads him to get a principle wrong, "is not a heretic. He is counted among the wise and devout of Israel, even though he is mistaken." He still needs atonement.
The Rambam's list is the one that entered the siddur. None of these voices says any of the thirteen is false. They argue about which beliefs are the foundations, and about what to call a person who honestly gets one wrong.
Mishnah Sanhedrin 10:1,Rambam, Commentary on the Mishnah, Sanhedrin 10:1,Rambam, Mishneh Torah, Laws of Repentance 3:7, with the Raavad's note,Sefer HaIkkarim 1:2, 1:4 and 4:42If God has no body, how did Moshe "look at His likeness"?
Line 3 says God has no body and nothing like a body. Four lines later, Moshe is the prophet who "looked at His likeness." It sounds like the poem contradicts itself.
The poet is quoting. "He looks at the likeness of Hashem" is what God says about Moshe in Bamidbar 12:8. And the same Torah says about Mount Sinai, "You saw no likeness at all" (Devarim 4:15). That is the verse the Rambam brings for this principle. So the question is really about the Torah.
Rashi answers from the Torah itself. When Moshe asked to see God's glory, he was told: "You cannot see My face." What he was shown, the Torah calls "My back." That, says Rashi, is the "likeness" in our verse.
The Rambam explains what "face" and "back" can mean when there is no body. In the Mishneh Torah, his law code, he writes that the hands, eyes and ears of God in the Torah are all figures of speech. "The Torah speaks in human language," because bodies are all that people know. His proof is that the prophets describe different things. One saw white clothing, another saw red. Moshe himself saw a warrior at the sea and, at Sinai, someone wrapped like a prayer leader. That shows, he says, that there is no actual shape. It is all prophetic vision.
So what did Moshe get? The Rambam says Moshe wanted to know God the way you know a person whose face you have seen, so clearly that you could never mix him up with anyone else. He was told that no living human can. What he received was like recognizing someone from behind: more than any person before or after him ever knew, enough to tell apart from everything else, and still not the face.
So the "likeness" in line 7 is not a picture. It is the closest any human mind ever came, and even that was partial. Line 3 still stands.
Bamidbar 12:8 with Rashi,Devarim 4:15,Rambam, Commentary on the Mishnah, Sanhedrin 10:1, Principle 3,Shemot 33:18-23,Rambam, Laws of the Foundations of the Torah 1:9-10It says God repays good and evil. So why do good people suffer?
Line 11 sounds like a simple deal: do good and get good, do evil and get evil. Anyone who has looked around knows that life does not always work that way. The people who wrote our sources knew it too.
The Gemara tells of a son who fell and died on his way back from doing two commandments for which the Torah promises a long, good life. Rabbi Yaakov's conclusion: the reward for a commandment is not paid in this world. The promise is about "the world that is entirely good." (The story is told at Eilu Devarim.)
The Rambam's wording of the principle points the same way: God rewards and punishes, "and the great reward is the World to Come." Read that way, line 11 is about how things finally come out, not about what you can see this week.
Even so, the question did not go away. According to the Gemara, Moshe himself asked God why some good people have it good and some have it bad. One opinion there says he was given an answer. Rabbi Meir disagrees: this was the one request that was not granted.
And in Pirkei Avot (the part of the Mishnah that collects the Sages' sayings on how to live), Rabbi Yannai says: "It is not in our hands, neither the calm of the wicked nor the suffering of the righteous." Rabbi Ovadiah of Bartenura, in his standard commentary on the Mishnah, gives this as the first meaning: we do not know why.
So the line states a trust that what a person does matters to God and will be answered. It does not claim that the world already looks fair. Our sources say both things, and they do not pretend the second one is easy.
Kiddushin 39b,Rambam, Commentary on the Mishnah, Sanhedrin 10:1, Principle 11,Berakhot 7a,Pirkei Avot 4:15 with Bartenura