As the world awaits Mother Teresa’s canonization Sunday, one mystery remains: why the international Left still harbors such hatred for a diminutive religious sister who spent her entire life serving the poorest of the poor.

After all, with her inexhaustible dedication to alleviating poverty and assisting the needy, Mother Teresa should be an icon of liberals the world over. Instead, we find that the Left showers her not with affection and praise, but with scorn and disdain.

On September 1, The Washington Post published an article titled “Why Mother Teresa Is Still No Saint to Many of Her Critics,” citing harsh condemnations of the nun by Hindu nationalists and cataloguing the complaints lodged against the missionary’s work through the decades.

Earlier this year, Salon called Mother Teresa “repugnant,” accusing her of glorifying suffering instead of relieving it. “Judged by any metric of medical standards,” the piece stated, “it is difficult to remember her legacy as anything other than an inefficient, sanctimonious and wholly ideological franchise.”

Last weekend, The New York Times showcased “one of the most vocal critics” of Mother Teresa, an Indian physician named Aroup Chatterjee who has made a career out of casting aspersions on the work of the Albanian nun.

Chatterjee calls Teresa’s work “an imperialist venture of the Catholic Church against an Eastern population.”

“I just thought that this myth had to be challenged,” he added.

In 1994, Dr. Chatterjee teamed up with professional atheist Christopher Hitchens to produce a documentary trashing Mother Teresa and her missionaries, called “Hell’s Angel.”

Shortly afterward, Hitchens cashed in on Mother Teresa’s immense popularity by writing his own bestselling book excoriating the sister, irreverently titled The Missionary Position.

In this “exposé,” Hitchens calls Mother Teresa “a religious fundamentalist, a political operative, a primitive sermonizer, and an accomplice of worldly secular powers,” as well as asserting that the secret ulterior motive behind all her work was “furthering Catholic doctrine.”

So the questions again present themselves: Why so much hatred? Why so much deep-seated anger against this woman?

Sifting through the literature dedicated to smearing the legacy of Mother Teresa, one discovers that all the arguments against her really boil down to two, which the Left can never forgive: her vocal and intransigent opposition to abortion and her overtly Christian spirituality that moved her to pour herself out for her fellow man.

All the other reasons given—that she provided inferior health care, that she was occasionally irritable with coworkers, that she accepted donations from morally ambiguous characters—are really just a cover for the two that irked the Left to the point of hysteria.

And hysteria it has been.

In a noteworthy 1986 essay published by the international abortion giant Planned Parenthood, titled “Mother Teresa, the Woman of My Nightmares,” one gets a taste of the profound odium stirred up by this simple religious sister.

“This very successful old and withered person, who doesn’t look in the least like a woman, especially when she raises her clenched fists in prayer, and who, for us, is a very suspect holder of the Nobel Prize,” Planned Parenthood wrote in its official publication Sexualpedagogik, “has become for us the symbol of all that is bad in motherhood and womanhood, an image with which we do not wish to be associated.”

“You, you nightmare of women! You unliberated, enslaved wives, mothers, nuns and aunts, what do you want from us, who have finally decided that we are going to take control of our bodies, our children, and our destiny into our own hands?” it ran.

Abortion, in fact, formed the centerpiece of Mother Teresa’s definition of poverty and all that is wrong with the world. The three most public speeches of her career—her acceptance of the Nobel Peace Prize, her Harvard Commencement address, and her words at the National Prayer Breakfast in Washington, D.C.—all focused on abortion as the greatest social injustice in the world today.

For Mother Teresa, the voiceless unborn child was truly the “poorest of the poor,” who deserves our undying respect and protection.

In her acceptance speech for the Nobel Peace Prize in 1979, for instance, she dared to say, “I feel the greatest destroyer of peace today is abortion, because it is a direct war, a direct killing – direct murder by the mother herself.”

At the National Prayer Breakfast in 1994, the politically incorrect sister told then-President Bill Clinton and his wife Hillary that abortion is a “war against the child.”

“And if we accept that a mother can kill even her own child, how can we tell other people not to kill one another?” the nun continued.

“By abortion, the mother does not learn to love, but kills even her own child to solve her problems,” she said. “Any country that accepts abortion is not teaching its people to love, but to use any violence to get what they want.”

But opposition to abortion was not the only crime that earned Mother Teresa the undying ire of the Left. She was also irritatingly… religious. Instead of secular philanthropy, she engaged in old-school Christian charity, picking the dying up off the street and holding them in her arms as they passed away, for the love of God.

Mother Teresa was guilty, in fact, of the great modern sin of political incorrectness. She freely and unapologetically invoked her love for Jesus Christ as the reason behind everything she did, a practice that is anathema to a world antiseptically cleansed from the grime of religious piety.

“I see Jesus in every human being,” she said. “I say to myself, this is hungry Jesus, I must feed him. This is sick Jesus. This one has leprosy or gangrene; I must wash him and tend to him. I serve because I love Jesus.”

Despite her spiritual motivations, however, Mother Teresa was an avowed enemy of proselytism in her work with the poor. She offered love and assistance to all, without ever making conversion a condition or even an aim of her care.

“We never try to convert those whom we receive to Christianity,” she said, “but in our work we bear witness to the love of God’s presence, and if Catholics, Protestants, Buddhists, or agnostics become for this better men—simply better—we will be satisfied.”

Teresa believed that those who find love find God, and that the best way to bring people to God is by sharing our love with them. “Let no one ever come to you without leaving better and happier,” she said. “Be the living expression of God’s kindness: kindness in your face, kindness in your eyes, kindness in your smile.”

As Pope Francis canonizes Mother Teresa of Calcutta Sunday morning, one group will not be standing by to join the applause: the disaffected Left who cannot forgive the Albanian nun for her deeply Christian charity or her staunch opposition to abortion.

Even in this “year of mercy,” some sins can never be forgiven.

Follow Thomas D. Williams on Twitter Follow @tdwilliamsrome