Internationally recognised singer Marina Prior will appear at St Paul's Anglican Church Castle Hill this Sunday to tell listeners how God put a new song in her mouth.

Ms Prior will sing a number of classical hymns during the 10 am service before sharing her testimony with the congregation.

The Australian diva, associated with successful stage shows like "Phantom of the Opera', "Les Miserables' and "The Secret Garden', is part of a guest service aimed at revealing what it means to live in the Kingdom of God.

The Rev John Gray says Ms Prior's participation is heady stuff.

"One of our volunteers is a personal friend of Marina and was able to tee it up. We’re just getting used to the idea ourselves," he says.

Youthworks CEO the Rev Al Stewart will deliver a message from Matthew 18 focussing on the humility at the heart of the Gospel.

Mr Gray says learning to "rise downwards' is essential if you are going to do business with God.

“Jesus said "If you want to be great in the kingdom of God, you have to be least of all.' So if you want to be great you have to "rise' downwards, by being a servant," he says.

"That idea should mark churches across the world."

St Paul's is extending an open invitation to Christians to bring friends to hear Ms Prior testimony and Mr Stewart's message of repentance.

"We don’t care where they come to church, so long as they end up in the Kingdom," he says.

St Paul's is located at 421 Old Northern Rd, Castle Hill.