In one sense one is serving Guru by serving Iskcon because Iskcon is a transcendental movement so one remains in devotional service and as long as one is situated in devotional service, one is still connected with the spiritual master. But there are different levels in which one can serve the spiritual master. Lord Caitanya had a servant who was such an expert servant that he already understood what the Lord wanted before the Lord even spoke about it. So the first - class servant is trying to do not what he wants to do, but do what the spiritual master wants him to do in Krsna Consciousness.For example, it is stated that there is one place that is higher than Vrindavan - that is the place assigned by the Guru.
(Kadamba Kanana Swami, South Africa 2009)
