Matthew Henry on Malachi 2:17:
They had denied him to be a holy God, and had asserted that concerning him which is directly contrary to the doctrine of his holiness. As he is a holy God, he hates sin, is of purer eyes than to behold it, and cannot endure to look upon it, Habakkuk 1:13. He is not a God that has pleasure in wickedness, Psalm 5:4. And yet they had the impudence to say, in direct contradiction to this, Every one that does evil is good in the sight of the Lord, and he delights in them. This wicked inference they drew, without any reason, from the prosperity of sinners in their sinful courses (see Malachi 3:15), as if God’s love or hatred were to be known by that which is before us, and those must be concluded good in the sight of the Lord who are rich in the world. Or this they said because they wished it might be so; they were resolved to do evil, and yet to think themselves good in the sight of the Lord, and to believe that he delighted in them, notwithstanding; and therefore, under pretence of making God not so severe as he was commonly represented, they said as they would have it, and thought he was altogether such a one as themselves. Note, Those who think God a friend to sin affront him and deceive themselves.