When we speak of the dust of the lotus feet of the Spiritual Master, we are speaking of humble approach to serve his instructions. Unless we humbly serve the instructions of the great soul, it is Krishna's arrangement the He never reveals Himself.
Service does not mean I do what I want, when I want. Sevice means, I do whatever makes Krishna happy.
Our supreme duty is to serve the residents of Vraja who are afflicated by Krishna ‘s departure to Mathura.
Service is also kirtana. Only singing is not kirtana. Then it automatically turns into remembering. This is the by-product.
Devotee do not want liberation, they only want to serve. Service here or service there doesn't matter. 'Let me always serve you', that is the mood of a devotee.
The different parts of a body work selflessly to serve one another and keep the body healthy. Similarly, a healthy society is one in which the different sections serve each other instead of selfishly trying to enjoy by themselves.