Servant and Master
Said the Gerer Rabbi: "We call our prayers 'Services' to demonstrate that we are servants of the Lord. The servant owns no property except what he receives from his master; he has no anxiety concerning the future, since he relies upon maintenance by his master in return for work. In our own relations with the Creator, we should fee like the servant towards his master, without pride in our possessions, and without anxiety if we lack them."
Source: Siach Sarfei Kodesh