What atheists rarely understand is that while religion is a belief system, it is not something easily jettisoned. First, religions are not something unique to the individual; generally, it's a belief shared by a group. You can say "I have my own religion," but for most people it's something they recognize as a group belief even if they themselves have disengaged from religious belief.
Consider Spinoza. He was a member of the Jewish community. However, when his philosophical writings appeared to deviate from traditional Jewish thought, he was excommunicated by the Jewish community from which he came. But why was he excommunicated? It was because the community feared that the Chistians of that time and place would find his thoughts inimical to Christianity and that they would attack not only him but the entire Jewish community. But, regardless of what he wrote, Spinoza today is still considered very much a Jew.
We understand a love of Israel to be an integral part of Jewish belief. Jewish prayer books from earliest times refer to the Jewish love of Jerusalem, the cornerstone of Israel . It is mentioned in Jewish writings from very early times.. It was where King Solomon built the Jewish temple. The temple was destroyed by the Babylonians, but it was rebuilt by King Herod. It's final destruction came at the hands of the Romans, who expelled the Jews and renamed the land Palestine. it's a story known to every practicing Jew.
Does one's identification with this story and the Torah where the story of Judaism is found make one Jewish? Most likely, yes. But it helps to have other signs of membership. If one is male, it's helpful to have been circumsized. It's also helps, regardless of gender, to have had a Jewish mother.
But then there's the biblical story of Ruth. She was a widow who wasn't born Jewish. However, she had a special friend, Naomi, who was Jewish and, I believe, also a widow. In any event Naomi told Ruth, that she was going back home to her people, a people of some Jewish tribe. Ruth told Naomi she'd join her. Where Naomi went, Ruth wanted to go. If Naomi's tribe was Jewish, she'd be Jewish. Ruth ultimately married a Jewish fellow and had kids. They must all have been Jewish because her line extended to the great Jewish king, David.
It would seem that to be Jewish one simply has to identify as being Jewish. Some groups within Judaism aren't that casual about Jewish membership. For Orthodox jews, a person not Jewish, has to undergo an extensive educational program, be submerged in a mikva, and, if male, must get circumcized.
For people wishing to become Christian, it helps to get baptized. For Muslims, it's only necessary to express a wish to be Muslim. Leaving the Muslim faith is more complicated. In some places, rejection of Islam brings with it a death sentence.
Each culture has it's own system of beliefs. Other religions believe in a multiple of Gods. One such religion was that of the early Greeks. This religion was found to be so attractive that the Romans adopted it. They simply changed the names of the Gods from Greek to Latin.
In our day, elements of the religion are being shed. There was a time when people thought that the sun travelled around the earth. That proved to be incorrect. Other stories like Adam and Eve, and Noah's ark also began to be questioned. And why were there no dinosaurs in our the tales of creation? It became apparent that considerable reinterpretation was required.
The main feature of religion today are it's lessons of morality. Hillel's requirement for becoming a Jew was to stand on one foot and proclaim you would not do another what you didn't want others to do unto you. To be a Christian, Jesus told his followers to do unto others as you would want done unto you. The two admonitions are similar, but do differ slightly in tone.
The problem we run into with religion is with someone respecting the religion of another. Christians historically have had a problem with people who refused to acknowledge Jesus as being, not only the son of God, but a man who actually became God. The Islamic view is that people not acknowledging Mohammed as the last prophet of God where either people of the Book by which they meant either Christians or Jews, or others. The "others" were considered heretics and, where feasible, put to death.
People of the book were viewed by Muslims as dhimmi, or second-class citizens. On them a special tax was levied. And, depending on where they lived, certain privileges were denied them such as the building of churches and synagogues. However, it must be acknowledged that many Muslims today have progressed in their system of beliefs and live in harmony with both Christians and Jews. Strict atheists have any number of paths to follow among religious people and still live with them in harmony. It's not unreasonable for one to be an atheist but yet take pride in the teachings of Judaism.
