Jamieson, Fausset and Brown on Malachi 3:13-18

13-18. He notices the complaint of the Jews that it is of no profit to serve Jehovah, for that the ungodly proud are happy; and declares He will soon bring the day when it shall be known that He puts an everlasting distinction between the godly and the ungodly.

words ... stout--Hebrew, "hard"; so "the hard speeches which ungodly sinners have spoken against Him" (Jude 15) [Henderson].

have we spoken--The Hebrew expresses at once their assiduity and habit of speaking against God [Vatablus]. The niphal form of the verb implies that these things were said, not directly to God, but of God, to one another (Eze 33:20) [Moore].