The staggering of senatorial elections was intended to insulate senators from shifts in:

Staggering senate elections have the benefits of protecting senators and senate from staggering public sentiment

Public sentiment is dynamic and not static. This means it keeps on changing from time to time. To insulate the senate, senators are elected for a term of six years, and every two years, a third of the senators are reelected. this means there is continuity of policies in the house, and senators remain committed to nationalistic agendas.