Srila Prabhupada says:
Rama and Krishna are names of God, and Hare is the energy of God. So when we chant the maha-mantra, we address God together with His energy. This energy is of two kinds, the spiritual and the material. At present we are in the clutches of the material energy. Therefore we pray to Krishna that He may kindly deliver us from the service of the material energy and accept us into the service of the spiritual energy. That is our whole philosophy. Hare Krishna means, “O energy of God, O God [Krishna], please engage me in Your service.” It is our nature to render service. Somehow or other we have come to the service of material things, but when this service is transformed into the service of the spiritual energy, then our life is perfect.
HARE KRISHNA MAHAMANTRA