Structural functionalism holds that every aspect of a society has a function in keeping that society working properly. Therefore, a structural functionalist take on religion would emphasize that religion contributes to the stability of a society. A functionalist might point out, for example, that shared religious values are an important part of maintaining social cohesion. Such a scholar might also argue that religion helps to maintain social order. Religion can encourage people to see society's rules (like respect for private property or sticking with and supporting one's family) as rules that are actually handed down by a higher being.
In either case, the point is that a structural functionalist would argue that religion plays an important part in keeping society functioning properly.