Avoiding offenses to devotees of Krsna is the first and one of the most important offenses to avoid. We tend to get familiar with our spiritual associates and may make offenses or with ease criticise this devotee or that. This is due to our bodily concept of life, thinking we are this body and basing our thinking on this. When we chant well....this bodily concept melts and we see each other as a spiritual soul and a servant of the Lord.
In terms of spiritual life, this offense is one of the biggest impediments for achieving the taste for chanting the Holy names. We need this reminder - that somehow or other we have to avoid offenses to devotees and then we can more easily avoid the other offenses by the Lord's grace.
"When a mad elephant enters a garden, it spoils all the fruits and flowers. Similarly, if one offends a Vaisnava, he spoils all his spiritual assets." SB 5.10.17 purport