Jamieson, Fausset and Brown on Malachi 2:17

17. wearied ... Lord--(Is 43:24). This verse forms the transition to Mal 3:1, &c. The Jewish skeptics of that day said virtually, God delighteth in evil-doers (inferring this from the prosperity of the surrounding heathen, while they, the Jews, were comparatively not prosperous: forgetting that their attendance to minor and external duties did not make up for their neglect of the weightier duties of the law; for example, the duty they owed their wives, just previously discussed); or (if not) Where (is the proof that He is) the God of judgment? To this the reply (Mal 3:1) is, "The Lord whom ye seek, and whom as messenger of the covenant (that is, divine ratifier of God's covenant with Israel) ye delight in (thinking He will restore Israel to its proper place as first of the nations), shall suddenly come," not as a Restorer of Israel temporally, but as a consuming Judge against Jerusalem (Am 5:18, 19, 20). The "suddenly" implies the unpreparedness of the Jews, who, to the last of the siege, were expecting a temporal deliverer, whereas a destructive judgment was about to destroy them. So skepticism shall be rife before Christ's second coming. He shall suddenly and unexpectedly come then also as a consuming Judge to unbelievers (2Pe 3:3, 4). Then, too, they shall affect to seek His coming, while really denying it (Is 5:19; Jr 17:15; Eze 12:22, 27).