Each of the five main U.S. employment-based immigrant visa classes (permanent resident visa classes) covers a very different group of workers/immigrants. The EB-4 class is the class for "special immigrants." This class is somewhat unique among the employment-based visa classes, because rather than covering a general class of individuals, it covers a collection of very specific types of workers/immigrants.
To qualify for this visa class, an individual must fall under the definition of a "special immigrant." Religious workers are among those who can fall under the special immigrant designation, but they are certainly not the only ones. Other individuals that could qualify to be a special immigrant for EB-4 purposes include: special immigrant juveniles, members of the armed forces, broadcasters, physicians, international organization employees, Iraqis who have provided assistance to the U.S., Afghan or Iraqi translators, children/spouses of deceased NATO-6 employees, retired NATO-6 employees and Panama Canal Zone employees.
As one can see, the range of things that could qualify a person for EB-4 special immigrant permanent resident status is rather diverse. So, EB-4 applicants can have a very diverse range of individual circumstances. When a person who falls under one of the special immigrant classes is seeking an EB-4 visa, their specific personal characteristics and circumstances can have some considerable impacts.
For one, they could impact what the application process for the visa would involve. For example, generally, individuals seeking EB-4 status have to have their employer petition for them. However, there are some special exceptions to this under which individuals with certain circumstances can qualify to self-petition for an EB-4 visa.
Also, an EB-4 seeker's circumstances can impact how long they would likely have to wait to get an EB-4 visa if they meet all the eligibility requirements. One of these circumstances is what country they are from. This is because there are visa-per-country limits that the U.S. puts in place when it comes to EB-4 visas. So, if a person seeking EB-4 status is from a country for which the limit has already been reached for the year, they could end up having a substantial wait in front of them.
Source: U.S. Citizenship and Immigration Services, "Employment-Based Immigration: Fourth Preference EB-4," Accessed June 28, 2016