The Lord’s Prayer, in the words he gave the Apostles.
Seven petitions, given by Jesus himself when the disciples asked him how to pray.
When: Every day, at Mass before Communion, and at the start of each decade of the Rosary.
Why: The Catechism calls it the summary of the whole Gospel. Every other prayer is measured against it.
Our Father, who art in heaven, hallowed be thy name; thy kingdom come, thy will be done on earth as it is in heaven. Give us this day our daily bread, and forgive us our trespasses, as we forgive those who trespass against us; and lead us not into temptation, but deliver us from evil. Amen.