Why was excommunication one of the worst punishments?

excommunicated from the church was outlawed, believers could not help him, give shelter, worship was prohibited, it was impossible to bury, baptize, and that means everyone was doomed to hellish torments.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.