PORTLAND – My son is 4½ years old, but he is already an expert on a lot of things. He knows all about the dinosaurs and even about the Tyrannosaurus rex. T. rex inhabited the Earth in the “Curvaceous Period,” as he calls it. It was before my time, so I can’t really argue with my son, the expert.

But sometimes we can call his grandparents for confirmation on the details.

The other day, my son came home and told me about a man called Martin Luther King Jr. We called “Savta,” the Hebrew word for “grandmother,” to find out some more. From her, we learned that in the ancient era, there was a strange law in America that allowed for racial segregation.

Savta told us that she once saw water fountains and swimming pools in Virginia with signs that said “White people only.” So-called “colored” people, or black people, were not allowed to drink from the same water fountains as the majority white population. In some places, black people were not allowed to sit in the front of the bus, which was reserved for the white people.

The Rev. Martin Luther King Jr. helped overturn these laws through peaceful protests and civil disobedience.

As Savta talked about the ancient past, it was hard to tell if what she was saying actually happened. Why would anyone want to discriminate against someone because of the color of his or her skin? What a strange and hateful idea.

But the other day, I received a hate email in my inbox. The woman wrote to me to say that she was considering joining our synagogue, but she was offended by something on our website.

Our website says, “Our synagogue celebrates Martin Luther King day, in honor of the man who has provided the world with guidance on how to accord respect to each human being in the world.” The woman wrote to me using racist terms about the Rev. Martin Luther King Jr. and even about the president of the United States.

The woman, who lives right here in Maine, is not crazy. She is clinging to ideas of racial hatred and fears of other racial groups that have been a part of human history for many centuries of the distant past. The vitality of these ideas has not disappeared from life, unlike the dinosaurs of millions of years ago.

As a parent, I know that I, with the help of my wife and our parents, and with the help of our children’s schoolteachers, must do the best I can to teach our children about the hateful racism of the past that still persists in various life forms, so that we all can learn to respect human beings in the present, without judgment based on the color of skin.

For me as a rabbi, the words and teachings of the Rev. Martin Luther King Jr. go far beyond a call for racial equality. His most powerful words to me are those that he wrote from a Birmingham city jail.

When demonstrators took to the streets to protest racial injustice in Alabama, rabbis and priests in Birmingham tried to stop the protesters. The religious leaders signed a letter declaring that the demonstrations against racial injustice in the city were “unwise and untimely.” They asked the “outsiders” to go away, and they asked their congregants to “withdraw support from these demonstrations.”

The local bishops, ministers and rabbis in Birmingham wished for quiet and asked that the demonstrators turn to the courts to accomplish their goals.

The Rev. King wrote from jail, “I felt that the white ministers, priests and rabbis of the South would be among our strongest allies,” but instead they were the “opponents.” Those who preached caution from behind “the anesthetizing security of stained-glass windows” were causing “shattered dreams.”

The Rev. King wrote of his disappointment in organized religion in the city, as well as in the religious leaders who supported the local police force as they attacked the demonstrators.

I frequently think about the words that the Rev. King wrote from his jail cell.

Sometimes we need to overturn laws in society and give voice to ideas that might be unpopular and unsettling, because if we don’t, the temple of stained glass can be dismissed as “an irrelevant social club with no meaning for the twentieth century.”

The life and words of the Rev. King are so inspiring. He lived long ago and wrote of a distant tomorrow, but his message to each of us in the present should be enduring and real.

Rabbi Akiva Herzfeld leads Congregation Shaarey Tphiloh in Portland.