This is a fairly late feast, going back only to the 13th or 14th century. It was established widely throughout the Church to pray for unity. The present date of celebration was set in 1969 in order to follow the Annunciation of the Lord (March 25) and precede the Birthday of John the Baptist (June 24).
Like most feasts of Mary, it is closely connected with Jesus and his saving work. The more visible actors in the visitation drama (see Luke 1:39-45) are Mary and Elizabeth. However, Jesus and John the Baptist steal the scene in a hidden way. Jesus makes John leap with joythe joy of messianic salvation. Elizabeth, in turn, is filled with the Holy Spirit and addresses words of praise to Marywords that echo down through the ages.
It is helpful to recall that we do not have a journalists account of this meeting. Rather, Luke, speaking for the Church, gives a prayerful poets rendition of the scene. Elizabeths praise of Mary as the mother of my Lord can be viewed as the earliest Churchs devotion to Mary. As with all authentic devotion to Mary, Elizabeths (the Churchs) words first praise God for what God has done to Mary. Only secondly does she praise Mary for trusting Gods words.
Then comes the Magnificat (Luke 1:46-55). Here Mary herself (like the Church) traces all her greatness to God.