The phrase 'subject of devotion' is correct and can be used in written English.
It usually refers to someone or something that someone is devoted to. For example, "My mother is the subject of my deepest devotion."
Mr. Dufour had cooked and been a partner at Au Pied de Cochon, a Montreal restaurant that is the subject of devotion in the food-crazy set for its commitment to excess.
There was not much of crowd yet, actually, but thousands of people are expected over the weekend to honor and pray before a relic tied to Our Lady of Guadalupe, a beloved and venerated symbol for Hispanic Catholics, a source of Mexican national identity and an increasing subject of devotion for non-Hispanics.
There are numerous depictions of the Virgin and Child, reflecting the Virgin's contemporary popularity as a subject of devotion.
The prevalence of trichophilia (hair partialism or fetishism) is 7% in the population, and very long hair is a common subject of devotion in this group.
It was an album that received the most rapturous critical reception, and whose songs became the subject of great devotion.
The biggest dream of all cultural fanclubs – the discovery of a lost work by the subject of their devotion – now crowns the birth centenary celebrations of Arthur Miller.
Mr. Dufour had cooked and been a partner at a Montreal restaurant, Au Pied de Cochon, that is the subject of considerable devotion in the food-crazy set for its commitment to foie gras and excess.
It is a matter of devotion.
One reflection of this sense of the autonomy was the rules change, in 1758, in the Académie Française's eloquence competitions: orators previously required to give speeches on subjects of religious devotion were now asked to deliver eulogies of "great men of the nation".
Crab has been the subject of Lance's devotion since he was a puppy: he was "one that I saved from drowning, when three or four of his blind brothers and sisters went to it … Nay, I'll be sworn, I have sat in the stocks for puddings he hath stolen, otherwise he had been executed; I have stood on the pillory for geese he hath killed, otherwise he had suffered for't".
Writer attests to proof of his subject's devotion to friends in the originality of a hymn, written in iambic pentameter for the marriage of mutual friends.
