'Solemn Assembly' in the Bible

Consecrate a fast,Proclaim a solemn assembly,Gather the eldersAnd all the inhabitants of the landTo the house of the Lord your God,And cry out to the Lord [in penitent pleadings].

Blow a trumpet in Zion [warning of impending judgment],Dedicate a fast [as a day of restraint and humility], call a solemn assembly.