Final answer:
The principal part of a church, extending from the narthex to the choir or chancel and flanked by aisles, is called the nave.
Step-by-step explanation:
The principal or central part of a church, extending from the narthex to the choir or chancel and usually flanked by aisles, is called the nave. The nave is the long hallway in the shape of a cross in a church, and it is crossed by the transept. The nave is where the congregation sits during a church service, and it is usually the most spacious area of the church. The narthex is the entrance area of the church, the choir is the space behind the altar of the church, and the chancel is the area around the altar. Both the choir and chancel are part of the church's sanctum.