Complete Commentary on the Whole Bible, by Matthew Henry, at sacred-texts.com
(Mal 4:1-3) The judgements on the wicked, and the happiness of the righteous.
(Mal 4:4-6) Regard to be had to the law; John the Baptist promised as the forerunner of Messiah.
Here is a reference to the first and to the second coming of Christ: God has fixed the day of both. Those who do wickedly, who do not fear God's anger, shall feel it. It is certainly to be applied to the day of judgment, when Christ shall be revealed in flaming fire; to execute judgment on the proud, and all that do wickedly. In both, Christ is a rejoicing Light to those who serve him faithfully. By the Sun of Righteousness we understand Jesus Christ. Through him believers are justified and sanctified, and so are brought to see light. His influences render the sinner holy, joyful, and fruitful. It is applicable to the graces and comforts of the Holy Spirit, brought into the souls of men. Christ gave the Spirit to those who are his, to shine in their hearts, and to be a Comforter to them, a Sun and a Shield. That day which to the wicked will burn as an oven, will to the righteous be bright as the morning; it is what they wait for, more than those that wait for the morning. Christ came as the Sun, to bring, not only light to a dark world, but health to a distempered world. Souls shall increase in knowledge and spiritual strength. Their growth is as that of calves of the stall, not as the flower of the field, which is slender and weak, and soon withers. The saints' triumphs are all owing to God's victories; it is not they that do this, but God who does it for them. Behold another day is coming, far more dreadful to all that work wickedness than any which is gone before. How great then the happiness of the believer, when he goes from the darkness and misery of this world, to rejoice in the Lord for evermore!
Here is a solemn conclusion, not only of this prophecy, but of the Old Testament. Conscience bids us remember the law. Though we have not prophets, yet, as long as we have Bibles, we may keep up our communion with God. Let others boast in their proud reasoning, and call it enlightening, but let us keep near to that sacred word, through which this Sun of Righteousness shines upon the souls of his people. They must keep up a believing expectation of the gospel of Christ, and must look for the beginning of it. John the Baptist preached repentance and reformation, as Elijah had done. The turning of souls to God and their duty, is the best preparation of them for the great and dreadful day of the Lord. John shall preach a doctrine that shall reach men's hearts, and work a change in them. Thus he shall prepare the way for the kingdom of heaven. The Jewish nation, by wickedness, laid themselves open to the curse. God was ready to bring ruin upon them; but he will once more try whether they will repent and return; therefore he sent John the Baptist to preach repentance to them. Let the believer wait with patience for his release, and cheerfully expect the great day, when Christ shall come the second time to complete our salvation. But those must expect to be smitten with a sword, with a curse, who turn not to Him that smites them with a rod. None can expect to escape the curse of God's broken law, nor to enjoy the happiness of his chosen and redeemed people, unless their hearts are turned from sin and the world, to Christ and holiness. The grace of our Lord Jesus Christ be with us all. Amen.