The author of BELIEBER: Fame, Faith and the Heart of Justin Bieber is calling on the pop idol to remember his responsibility to young fans after he was recently snapped smoking what appeared to be weed.
Cathleen Falsani described her open letter, published on CNN, as a "wellbeing check from someone who genuinely cares".
She praised the way in which Bieber, a Christian, was "keenly aware" of the gifts given to him and "who bestowed them on you".
"With a perspective and sense of responsibility far beyond your years, throughout your public life thus far you have articulated beautifully and clearly your gratitude for the extraordinary favour and experiences you have had and continue to have as the most famous teenager on the planet," she said.
"And you have given thanks publicly and consistently to your supporters, the team that manages your business, mentors, creative partners, and your God."
Falsani also paid tribute to the star for encouraging fans to recognise the blessings in their own lives and give back.
However, she cautioned that when young fans see images of him with a butt in his hand or drinking, the "message they receive is inconsistent and confusing".
"You do have the choice to disregard your responsibilities. But you don't have the choice to avoid the consequences of your actions," she writes.
Falsani also advised the 18-year-old to be "diligent to guard your heart and mind more now than ever" as he makes the transition to adulthood, and not go down the same destructive path as other child celebrities have done in the past.
"Justin, as has been your intention, you have been a positive influence on countless children and young people around the globe. And I believe that you will continue to be a force of light and joy as long as you don't choose to ignore the divine GPS located in your heart of hearts," she writes.
"Remember who you are, Justin. Remember who you were created to be. A city on a hill. Salt and light."