Transcendental service to the Lord is not mundane. The service attitude of the devotee gradually increases and never becomes slackened. Generally, in old age a person is allowed retirement from mundane service. But in the transcendental service of the Lord there is no retirement at all; on the contrary, the service attitude increases more and more with the progress of age. In the transcendental service there is no satiation, and therefore there is no retirement. Materially, when a man becomes tired by rendering service in his physical body, he is allowed retirement, but in the transcendental service there is no feeling of fatigue because it is spiritual service and is not on the bodily plane. Service on the bodily plane dwindles as the body grows older, but the spirit is never old, and therefore on the spiritual plane the service is never tiresome.
Purport SB 3.2.3