As a kshatriya has no problems while taking the wounds on his chest. similarly a devotee has no problems taking wounds while serving Krishna.
A general instruction of the spiritual master becomes a personal and specific instruction for a sincere disciple.
To love to preach is one thing and to love those whom we preach is quite different.
A devotee doing sense gratification out of material conditionings, if keeps on listening to pure devotees, soon becomes disgusted of sense gratification and gives it up, and so attains the pure devotion to krishna.