Charles Spurgeon Commentary Daniel 9:6

"neither have we hearkened unto thy servants the prophets, that spake in thy name to our kings, our princes, and our fathers, and to all the people of the land." — Daniel 9:6 (ASV)

Neither have we hearkened unto thy servants the prophets, which spake in thy name to our kings, our princes, and our fathers, and to all the people of the land.

It greatly increases sin when we sin against warnings sent from God. Daniel confesses this.