Malachi 3:14

Ye have said, It is vain to serve God - They strove to destroy the Divine worship; they asserted that it was vanity; that, if they performed acts of worship, they should be nothing the better; and if they abstained, they should be nothing the worse. This was their teaching to the people.

Walked mournfully - Even repentance they have declared to be useless. This was a high pitch of ungodliness; but see what follows; behold the general conclusions of these reprobates: -