The phrase “praying the Catechism” is at least as old as Luther’s writings on the subject. I don’t know if the following contribution to the subject is original, but I haven’t come across it before.
The Catechism (in the narrower sense: The Commandments, Creed and Lord’s Prayer) can be prayed very simply and very quickly by praying the Lord’s Prayer. Conversely, the Lord’s Prayer is merely a summary of the Catechism – and thus can form the basis of an extended prayer life.
The Lord’s Prayer is simply the rest of the Catechism in prayer form. Let me demonstrate:
1st petition: Our Father who art in heaven
1st commandment: I am the Lord your God
2nd pet: Hallowed be Thy name
2nd comm: Do not misuse the name of the Lord your God
3rd pet: Thy kingdom come
3rd comm: Remember the Sabbath day to keep it holy
4th pet: Thy will be done on earth as it is in heaven
4th-10th comm: Love your neighbour as yourself
5th pet: Give us this day our daily bread
1st article: I believe in God … the maker of heaven & earth
6th pet: And forgive us our trespasses…
2nd art: And in Jesus Christ … was crucified, died … and rose again
7th pet: And lead us not into temptation but deliver…
3rd art: And in the Holy Spirit
This becomes even clearer when we read the Commandments and the Creed through the lense of the Small Catechism.