The worship of One God. Tradition traces this back to Abraham:
Abraham (18th century BCE) came from ancestry that had been God-fearing a couple of centuries earlier but had afterwards slipped into idolatry (Joshua 24:2). Nimrod, the idolatrous tyrant, had brought Abraham's father (Terah) from the Semitic ancestral seat near the conjunction of the Balikh and the Euphrates, and instated him in a position of power in his army in the royal Babylonian city of Ur. Nimrod persecuted any who would question his idolatrous cult.
The Kuzari (Rabbi Judah HaLevi, 1075-1141) states that Abraham was gifted with high intelligence; and, as Maimonides (1135-1204) describes, Abraham didn't blindly accept the ubiquitous idolatry. The whole populace had been duped, but the young Abraham contemplated the matter relentlessly, finally arriving at the conclusion that there is One God and that this should be taught to others as well. This is what is meant by his "calling out in the name of the Lord" (Genesis ch.12). As a young man, he remonstrated with passersby in public, demonstrating to them the falsehood of their idols; and our tradition tells how he was threatened and endangered by Nimrod. Later in life, God said to Abraham in prophecy to move to the Holy Land, which is where Abraham raised his family.
He continued his contemplations, eventually arriving at the attitudes and forms of behavior which God later incorporated into the Torah given to Moses. Abraham taught disciples (Talmud, Yoma 28b), gave tithes (Genesis ch.14), strove to raise a family (Genesis ch.15, 17, and 24) which would serve God, made a covenant with God (Genesis ch.15 and 17), welcomed guests into his home (Genesis ch.18) unlike the inhospitable Sodomites (Genesis ch.19), prayed for people (Genesis ch.18), rebuked others when necessary (Genesis ch.20), eulogized and buried the deceased (Genesis ch.23), and fulfilled God's will unquestioningly (Genesis ch.22). He became renowned as a prince of God (Genesis 23:6).
It is therefore clear why God expresses His love for Abraham (Isaiah 41:8) and calls Himself the God of Abraham (Genesis 26:24), and says that Abraham obeyed Him fully (Genesis 26:5). And this is why, according to our tradition, Abraham is credited with having founded the religion which became known as Judaism.
Shema is the most basic statement in Judaism, it's considered to be a radical statement because it's very important and needs to recite twice a day.
Study is necessary to know and follow the laws.
If it's in the Torah, it's basic to Judaism.
Kosher
the teachings of the Torah are Judaism.
The statement: That which is hateful to you, do not do to others.
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There are no particularly important symbols in Judaism, but the number ' 1 ' is quite significant.
Belief in One God.
the exodus
The Torah.
They all profess belief in a divine being as Creator.