"Let not your heart be disturbed. Do not fear that sickness, nor any other sickness or anguish. Am I not here, who is your Mother? Are you not under my protection? Am I not your health? Are you not happily within my fold? What else do you wish? Do not grieve nor be disturbed by anything."

(Words said by of Our Lady of Guadalupe to Juan Diego)

What comforting words for Juan Diego to hear. And, the Blessed Virgin Mary talked to him in his language, Nahuatl. She called him "Juanito, Juan Dieguito ", "the most humble of my sons"; "my son the least"; "my little dear". He was 57 years old, certainly an old age in a time and place where the male life expectancy was barely 40. Juan worked hard all his life and was an example of humility.

How it happened:

In 1523, just two years after the Aztec capital of Tenochitlan fell to Hernán Cortés and his Conquistadors, the first Roman Catholic missionaries arrivd to begin the religious conquest of Mexico.
Among their first converts was a man baptized with the Christian name Juan Diego. On the chilly morning of December 9, 1531, Juan Diego crossed the barren hill called Tepeyac to attend Mass. He was brought to a sudden halt by a blinding light and the sound of heavenly music. Before him appeared  an astounding vision--a beautiful dark-skinned woman who, calling the Indian "my son", declared herself to be the Virgin Mary, the mother of Jesus Christ. She told Juan Diego it was her desire to have a church built on Tepeyac hill, and asked him to relay that message to Bishop Juan de Zumarraga.It was no easy task for the humble Indian to be granted an audience with the top prelate, but the persistent Juan Diego was finally admitted. The incredulous Bishop demanded that he be provided with some proof of the unlikely encounter. Confused and fearful, Juan Diego avoided Tepeyac for several days, but on December 12, while rushing to find a priest to attend a seriously ill uncle, he took a short cut across the hill. The Virgin once again appeared and Juan Diego told her of the Bishop's request. The Virgin instructed him to pick roses from the usually barren and desolate hill and deliver them to Zumarraga as the sign.
Juan Diego gathered up the miraculous blossoms in his mantle and hurried off to complete his mission. Once again before the Bishop, he let the roses spill out before him. To the wonder of all assembled, a perfect image of La Virgen of Guadalupe was revealed emblazoned on Juan Diego's cloak.
Juan Diego's mantle, carefully preserved in the new Basilica, has been subjected to extensive analysis over the years. Experts have authenticated the fabric as dating to the 16th century, but have been unable to determine the type of pigment from which the image was rendered. It seems doubtful that in the Colonial era in Mexico human hands were capable of creating a portrait of its exquisite nature. It is even doubtful it can be done in Mexico today.  Most wonderous of all, after 465 years, the image of the Virgen de Guadalupe remains clearly imprinted on the miraculous cloak without visible signs of deterioration.
By order of the Bishop, a small church was soon constructed on the site designated by the Virgin. Skeptics are quick to point out the unlikely coincidence of the Virgin's appearance on Tepeyac, the very site of an Aztec temple dedicated to Tonatzin (earth godess, mother of the gods and protectress of humanity) which had been devastated by order of Bishop Zumarraga.
The original church was replaced by a larger structure built in 1709. The Miracle of Guadalupe was officially recognized by the Vatican in 1745. The second sanctuary was declared a Basilica in 1904. A new Basilica, of modern design and enormous capacity, was dedicated in October of 1976. This is found in the northern section of present-day Mexico City.
In this and other churches dedicated to La Virgen de Guadalupe throughout the nation, millions of the faithful will gather December 12 for processions, prayers, songs, dances, and fireworks to honor "La Reina de México" (the Queen of Mexico).
In essence, the Spanish conquest of 1519-1521 destroyed the core of Aztec religion-the cult of warfare and human sacrifice. The Aztecs were no longer able to feed the sun, yet the universe survived, and Huitzilopochtli was discredited. Aztec religion had lost its focus by 1531.
The Aztecs practiced human sacrifice on a wholesale scale.
We must remember that the Aztecs offered annually at least 20,000 men, women and children in human sacrifice to their gods. In 1487, just in a single 4 days long ceremony for the dedication of a new temple in Tenochtitlan, some 80,000 captives were killed in human sacrifice.

Why should the Virgin Mary appearing to an Indian in recently conquered Mexico and speaking to him in Nahuatl call herself "of Guadalupe", a Spanish name? Did she want to be called de Guadalupe because of the statue of Our Lady of Guadalupe in Estremadura, Spain? Because of Lupita who lived in Nuevo Laredo?  In all apparitions of the Blessed Virgin Mary she identified herself as the Virgin Mary and phrases like Mother of God or another of her titles, and was later usually known by the name of the place or region where she appeared (Lourdes, Fatima). So why should Mary, when appearing to an Indian in recently invaded Mexico and speaking in the local language, want to be named with the Spanish name of Guadalupe? Was she talking about the miraculous statue of Our Lady of Guadalupe, that was given by Pope Gregory the Great to the Bishop of Seville, was lost for 600 years and was found in 1326 by a cowherd guided by an apparition of Our Lady? The statue was named Guadalupe for the village located near the place of discovery. The origin of the name Guadalupe has always been a matter of controversy. It is nevertheless believed that the name came about because of the translation from Nahuatl to Spanish of the words used by the Virgin during the apparition to the ailing uncle of Juan Diego. It is believed that Our Lady used the Aztec Nahuatl word of coatlaxopeuh which is pronounced "quatlasupe" and sounds remarkably like the Spanish word Guadalupe. Coa meaning serpent, tla being the noun ending which can be interpreted as "the", while xopeuh means to crush or stamp out. So Our Lady must have called herself the one "who crushes the serpent¹." Serpent-god Quetzalcoatl. Certainly, in this case She crushed the serpent, and few years later millions of the natives were converted to Christianity. And the human sacrifices ended.
¹In is interesting to note that in Genesis 3:15 (in the Old Testament) it is indicated a woman would step on the serpent's head.

After the miracle of Guadalupe, Juan Diego moved to a room attached to the chapel that housed the sacred image, after having given his business and property to his uncle; and he spent the rest of his life propagating the account of the apparitions to his countrymen. He died on May 30, 1548, at the age of 74. Juan Diego said to the Blessed Virgin Mary: "I am a nobody, I am a small rope, a tiny ladder, the tail end, a leaf" as a model of humility for all of us.

In July of 2002 Juan Diego was canonized (declared a Saint) in the Basicila of the Virgin of Guadalupe in Mexico City.
The well known prayer Ave Maria has its roots in Luke I:42 where Elizabeth (who is Mary's cousin) salutes Mary and in Luke I:28 where the Arch Angel Gabriel salutes Mary.