4:4
(Verse 4.) Remember the law of Moses my servant, which I commanded him in Horeb for all Israel, with the statutes and judgments. Likewise in the Septuagint. The just retribution in the future will be righteous, when the flame will devour and burn the root and offspring of the proud, and the sun of righteousness will rise for those who fear the Lord, with healing in its wings. Therefore remember the law of Moses my servant, which I gave him on Mount Horeb, which is Sinai, for all Israel, with the statutes and judgments. But the Apostle says: We know that the law is spiritual (Rom. VII, 14); and blessed David: Open my eyes, and I will consider the wonders of your law (Ps. CXVIII, 18); and because all ate the heavenly manna in a spiritual manner, and the whole people of Israel drank from the same spiritual rock that followed them, and that rock was Christ. (I Cor. X, 3, 4); those who believe in Christ must spiritually observe the precepts of the law, which were given in Horeb (which means dryness), through which the moisture of all vices is dried up, and to the rays of the sun of justice, the rheum of lust is dried. But the Lord spoke to all of Israel, who understands with their heart God, and of whom it is said in the Gospel: Blessed are the pure in heart, for they shall see God (Matt. 5:8).
4:5-6
(Ver. 5, 6.) Behold, I will send you Elijah the prophet, before the great and dreadful day of the Lord comes: and he will turn the hearts of the fathers to the children, and the hearts of the children to their fathers, lest I come and strike the earth with a curse. LXX: Behold, I will send you Elijah the Tishbite, before the great and glorious day of the Lord comes: he will turn the heart of the father to the son, and the heart of man to his neighbor; lest I come and strike the earth completely. After Moses (whose commands we have taught are to be observed spiritually), Jesus says that Elijah must be sent: in Moses, the Law, in Elijah, signifying prophecy, as Abraham said to a certain wealthy man dressed in purple: They have Moses and the prophets, let them listen to them (Luke 16:29). And the Lord and Savior, transfigured on the mountain, was speaking with Moses and Elijah in radiant clothing, who were also telling him what he would suffer in Jerusalem (Mark 9): for the Law and the chorus of all the prophets proclaim the passion of Christ. Therefore, before the day of judgment comes, and the Lord strikes the earth with a curse, either utterly or suddenly, as the LXX translated it (for this signifies ἀρδὴν), the Lord will send Elijah (who is interpreted as 'my God' and is from the city of Thesbi, which means 'conversion' and 'repentance') to convert the hearts of the fathers to the children, namely, Abraham and Isaac and Jacob, and all the patriarchs, so that their descendants may believe in the Lord and Savior, in whom they also believed. For Abraham saw the day of the Lord and rejoiced (John 8:56), that is, the heart of the father to the son, that is, the heart of God to every one who has received the spirit of adoption. And the heart of the children to their fathers, like the Jews and Christians, who now disagree among themselves, may they agree equally in the religion of Christ. Hence it is said to the apostles, who spread the seed of the Gospel throughout the whole world: For your fathers have begotten sons for you (Ps. 44:17). For if Elijah does not convert the heart of the fathers to the children beforehand, and the heart of the children to their fathers, when the great and terrible day comes (great for the saints, terrible for sinners), the true and just judge will strike, not the heavens, nor those who dwell in heaven, but the earth with a curse, those who perform earthly works. The Jews and the Judaizing heretics believe that Elijah will come before their own Messiah and will restore all things. Hence, in the Gospel, a question is posed to Christ: Why do the Pharisees say that Elijah will come? To which He responded: Elijah will indeed come, and if you believe, he has already come, referring to John the Baptist as Elijah.