Mono White Devotion is held together by Heliod, Sun-Crowned. When active, he becomes a powerful beate. His lifegain synergies are active all the time, though.
The rest of the deck also focuses on lifegain synergies and protection for your best cards with Selfless Savior and Alseid of Life’s Bounty. One of the cards worth protecting is certainly Linden, the Steadfast Queen, which enables Heliod almost by herself..
If you like beating your opponents down while being at 50 life, you can’t go wrong with this one.