Why is the spiritual side of the kingdom necessary in addition to the physical aspect?
The spiritual side is necessary because the physical, literal, political aspect—granting peace and safety to the Jewish people—cannot alone grant entrance into the kingdom. As Jesus told Nicodemus in John 3, except a man be born again, or experience salvation, he cannot enter the kingdom. The two must come together.
Les explains that the kingdom first has the introduction of the physical, literal, political aspect, granting peace and safety to the Jewish people and deliverance from mortal, physical, next-door enemies so they might serve God without fear in holiness and righteousness. But then he says you also have to have the spiritual side, because Jesus told Nicodemus in John 3 that except a man be born again, or experience salvation, he cannot enter the kingdom. Therefore the physical and spiritual aspects have to come together.
Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God.