In the early Church, monks led services with a Latin recitation of the Psalms called, "The Psalter." But most people couldn’t read or write Latin, so the "Our Father" prayer was substituted so that people could easily pray together.
Tradition holds that St. Dominic combined the Our Father and Hail Mary prayers with meditations on the mysteries of our faith into the rosary we know today.
So the rosary makes it easy for us to pray together and to focus on Jesus’ life and glory.