Material sense gratification, sinful activity kills the propensity to serve Krishna.
When Nityananda accepts us as His, then there is no more sense gratification.
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.
Sense gratification distances us away from the Lord who is in the heart.
Sense gratification means we are using the instrument (human body) meant for Liberation and for our Bondage.