Judaism places more emphasis on action than belief. Nonetheless, there are commandments of belief and foundational assertions of faith upon which our actions must be based.
In his commentary on Mishnah Sanhedrin 10.1, the Rambam presents thirteen principles of faith. These fundamental beliefs represent the conceptual framework upon which Jewish observance and peoplehood rests. Though they were controversial in their time, they are now widely accepted as a baseline definition of Orthodox Jewish faith.
According to the Rambam,
When a person believes in all of these principles and his faith in them is clarified, he enters into the category of Israel; and it is then a commandment to love him and to have mercy upon him and to act with him according to everything which God, may He be blessed, commanded about a man towards his fellow, regarding love and brotherhood.
These principles are important not only in that they provide guideposts to determine if our own thinking has gone off track; they also guide our interactions with others. The Rambam seems to imply that a Jewish person who accepts these principles cannot be considered an idolator or an outsider to Judaism, but bears the rights and privileges shared by all Jews. It is halachically forbidden to marginalize such a person due to other beliefs, even if they are erroneous.
Here is a concise summary of the principles as the Rambam states them:
- Existence of the Creator. There exists a Being, perfect in existence, who is the cause of all beings; all that exists depends on Him, while His existence depends on nothing else.
- Absolute Unity. This God is One in a way unlike any other oneness.
- Incorporeality. He has no body or bodily properties; nothing corporeal applies to Him.
- Eternity. He is first and last; nothing precedes or outlives Him.
- Exclusive Worship. It is proper to serve, pray to, and follow only Him; not angels, spheres, stars, or anything created.
- Prophecy. God communicates to humanity through prophecy.
- Moses’ Prophecy. The prophecy of Moshe Rabbenu is true and of a categorically higher order than that of other prophets.
- Torah from Heaven. The entire Torah that is in our hands today is of divine origin, given through Moses.
- Torah’s Immutability. This Torah will not be exchanged or changed, nor will there be another from the Creator.
- Divine Knowledge. God knows the actions and thoughts of people.
- Reward and Punishment. He rewards those who keep the commandments and punishes those who transgress them.
- Messiah. The coming of the Messiah is true; one must await him and not think he will delay.
- Resurrection. There will be resurrection of the dead at the time God wills.
These principles are not obscure or difficult to understand. The Rambam states them well. One is advised to read the Rambam's full explanation of these principles and not just rely on this summary.