That dear friend is a wonderful question.
Fist lets add some right perspective to our conversation [B][I]: “Forbidden by Mt.6: 7” See Psalm 136: Repeats “For His Kindness endures forever” 26 TIMES [/I][/B] And there are other places where repetition takes place as well. So we must be specific and precise in our reply.
Matt.6: 7 “And in praying do not heap up empty phrases as the Gentiles do; for they think that they will be heard for their many words.”
Notice that Matthew refers to “gentiles” [he is speaking to a Jewish audience.] This is important because Mt. is a Levite [ a member of the lower Jewish priesthood] and knows that the Torah does repeat praise and worship at times. In effect Mt. is separating religious from secular practices.
For those that may not know the rosary; is begins with the Apostles Creed; a summation of our beliefs. The other prayers are the Lords prayer [ 6times], the Glory be [to the Trinity] also 6 times; and the “Hail Mary” [53 times]
Because post are limited in size I can’t share the words of each at this time. BUT each petition of the Hail-Mary is found in Luke’s Gospel; chapter one, so it is biblically grounded.
The entire Rosary is a “prayer of petition.” Meaning a plea for divine assistance. It is far MORE accurate to explain that these prayers are “intercessory” in nature, than to Mary or to Saint so and so. We are asking Mary [and at time various Saints] to plead our needs and wants before the throne of God, because they ARE in God’s presence, and because in doing so they: Mary and the Saints ADD there own pleas to and with ours; making them more effective and meaningful. These payers are NOT intended to stop with Mary of the saints; but are to be “hand delivered” by them on our behalf.
In order to have “vanity” have ANY role at all, it would be necessary for us to be vain in our attempts. The polar opposite is true; as prayers of intercession require [absolutely] ones humility to beg for help from someone other than ourselves. 1Thes.5: 17 “pray constantly“, Luke.18: 1 “And he told them a parable, to the effect that they ought always to pray and not lose heart.” Rom.1: 9 For God is my witness, whom I serve with my spirit in the gospel of his Son, that without ceasing I mention you always in my prayers,
So, vanity has No place in our prayer; and repetition is FACTUALLY NOT forbidden. I pray this brief explanation clarifies for you what your seeking? If not let me know.