The 31 year old said his son, Leo, who underwent a reconstructive operation on his skull last Wednesday, has left medical staff amazed by the speed of his recovery.
Writing on Instagram, the Australian: "I even overheard one nurse say, 'We've never seen a patient recover so quickly from this surgery (that he just had only three days ago!).
"Of course, these docs might be surprised and wonder how this could happen, but we are certain of the answer: prayer"
"To each of the thousands of you around the world, who have been praying for our son, from the bottom of our hearts, thank you."
Luke and his wife, Courtney, found out their son required the surgery after he was taken to hospital for a separate health issue.
The Sydney-born performer - who founded For King & Country with his brother, Joel - also praised the tirelessness of his spouse in praying for Leo.
He went on to say: "This has not been an easy journey and honestly, Leo's had quite a dramatic life so far, but I am completely blown away by my wife's consistency in such deep prayer.
"I'm a different man having witnessed her great faith in praying for his protection, and for blessings on his life.
"We could not be more joyful in bringing our little Leo home."