As the kohen gadol moved through the sanctuary, the bells tinkled and the people were able to keep track of him.
The Apocrypha says in the book of Ben Sira (Ecclesiasticus 45:9), “He compassed him (the high priest) with pomegranates of gold and with many bells round about, to send forth a sound as he went, to make a sound that might be heard in the Temple for a memorial to the children of his people”.
The congregation needed to be assured that the kohen gadol was carrying out his duties correctly. So much rested on the priest’s shoulders. The whole fate and destiny of the people depended on his faithfulness and integrity.
Today the kohanim have a more limited range of responsibilities, but it is still important that they perform their tasks properly, especially in blessing the people and in personally keeping away from things which kohanim should not do.
By extension, the same observation applies to rabbis (how well they teach, preach and lead can crucially affect the Jewish future) and officiants (how well they conduct the services can ensure or, God forbid, deny Divine blessing to the community).
In their own interests as well as those of the Jewish people and mankind congregations should say the first Y’kum Purkan (the one for the rabbis) with special care.
In their own interests they should also internalise the sermons and d’rashot carefully, and when the chazan davens, make certain they say Amen.