Based on the purpose of the letter, Selim’s description of the followers of Shah Ismail I as a “heretical faction” can best be interpreted as a commentary of the Safavid Empire’s

The right response is "adherence to Shi'a Islam ".

Explanation:

Shi'a Islam has been broken across three different branches. The Twelvers, mentioned for their obedience to something like the twelve imams, are perhaps the most widespread as well as strongest. Throughout Iran, Azerbaijan, as well as Iraq, individuals constitute the bulk of the population. The word Shi'a applies mostly to Twelver Shi'a.