I will have compassion on those who fear the Lord, then you will again see the distinction between the just and the wicked. One of the main concerns of the book of Prophet Malachi is answering the age-old question of God’s justice. Why was it looking like God was turning a blind eye on the evil deeds of the wicked? Why was God not coming to the aid of those who were keeping his laws and statutes? Where was the much celebrated justice of God? As quoted by the Lord, the people were complaining that it was profitless to keep the Lord’s command since the evil doers were prospering with impunity (cf. vs. 14-15). In his  defense, the Lord reiterates his fidelity to the promises he had made to Israel. And even though the people had often strayed from the path set for them by the Lord, they were still God’s people. 
God’s justice had always been a controversial issue for the Israelites because of its  unreliability. The Lord was always seen to be slow in punishing the wicked as well as in rewarding the righteous. However, the Lord always reminded the Israelites that the  unreliability of his justice was also for their own benefit, for they too were never constant in their fidelity to God. Far from their understanding, God’s justice is not only about rewarding the righteous and punishing the wicked. Rather, God’s justice is more about salvation of God’s creatures. As such, if God’s justice is “slow” in coming, it is because God is in no hurry to send the perceived evildoers to the netherworld. God’s justice is thus properly executed when the wicked turn away from their evil ways in order to walk in the path of righteousness.