If the temple that Nephi built was fashioned after the temple of Solomon, as Nephi says (2 Nephi 5:16), then there would have been an outer court, the inner tabernacle, or holy place, and the holy of holies. This was the pattern for the tabernacle of Moses and was repeated again for the temple of Solomon, "A comparison of the plan of Solomon's Temple with that of the earlier Tabernacle shows that in all essentials of arrangement and proportion the two were so nearly alike as to be practically identical. True, the Tabernacle had but one enclosure, while the Temple was surrounded by courts, but the inner structure itself, the Temple proper, closely followed the earlier design." (James E. Talmage, The House of the Lord, p. 7)Therefore, in the temple of Solomon, like the tabernacle of Moses, there were three different areas which were representative of the three degrees of glory: outer court=telestial, holy place=terrestrial, and holy of holies=celestial. Traditionally, the people could enter the outer court but only the priests could go into the holy place. Entrance to the holy of holies was restricted to the high priest who could only enter once a year.
If Jacob taught the people in the temple, it makes sense that he would have taught them in the outer room which represented the telestial kingdom. This would have been the only room big enough for a large gathering of people. If the Nephites followed the pattern of the Jews, then none of the people would have been allowed to enter the other parts of the temple unless they held the priesthood and were performing specific priesthood functions. In the days of Christ, when the Jews similarly gathered to hear the teachings of the Savior in the temple of Herod, they met in the corresponding outer courts.