It was used for teaching because the story of the life of the Blessed Mother of God is important, and that story agreed with the oral teachings of the Apostles, (known as Holy Tradition)and the teachings of the early Church. Just like the Gospel of Thomas, has valuable information, but certain parts of it are not accurate, etc.
You need to know about Artemis Diana of Ephesus. Mary was declared “Mother of God” by the Christian church in about 431AD at Ephesus, Turkey where the temple to the goddess, Artemus Diana whose sacred title was “Queen of Heaven”. Artemus Diana was called “the mother of us all” by here worshipers. Check out the temple to the goddess Artemus Diana in Ephesus, Turkey. Read the account in Revelation 2 about the church at Ephesus. Thou hast left they first love” is referring to their allowing the worship of the goddess Artemus Diana to infiltrate the church. The Catholic Church has allowed the same to happen.
"Ephesus was an important religious city. The Temple of Diana (or Artemus, as the Greeks called her) was considered one of the seven wonders of the ancient world. The goddess Diana was the patron of all the prostitutes and, with her many-bosomed image, represented fertility and sexuality. Many writers in ancient times described the immorality of the city.
"One pillar in the Ephesian economy was the production of silver images of Diana by the many silversmiths who plied their trade there. Devotees of this goddess brought much gain to the city (Acts 19:23-27). Black magic was also widely practiced in Ephesus."
The Madonna and child are fashioned after Isis and her son Horus. Another was Dmeter and her daughter Kore.
Another is Astarte, also known as Astarat and Astoreth both are incarnations of Ishtar and Inanna Semitic goddess worshiped by Syrians, Canaanites, Phoenicians, and Egyptians. Even King Solomon built a Temple to her near Jerusalem. Astarte was referred to in the Bible as “the abomination”.
1 Kings 11:5 For Solomon went after Ashtoreth the goddess of the Zidonians, and after Milcom the abomination of the Ammonites.
In 2 Kings God calls her an abomination. 2 Kings 23:13 And the high places that were before Jerusalem, which were on the right hand of the mount of corruption, which Solomon the king of Israel had builded for Ashtoreth the abomination of the Zidonians, and for Chemosh the abomination of the Moabites, and for Milcom the abomination of the children of Ammon, did the king defile.
Jeremiah castigates the people for making offerings to the queen of heaven. Jeremiah 7:18 The children gather wood, and the fathers kindle the fire, and the women knead their dough, to make cakes to the queen of heaven, and to pour out drink offerings unto other gods, that they may provoke me to anger.
Make no mistake. The RCC worship of Mary is pagan based, not scriptural based.