1-5: The Lord demonstrates His love for Israel through a hypothetical conversation with His people. He points out His love for Jacob (Israel) over Esau (Edom) and reminds them how he has laid waste to Edom, their enemy.
6-14: God condemns the priests for offering polluted sacrifices on His altar. Offering a flawed, sick, or stolen animal was evil and caused God to become angry. It costed the one offering it nothing and profaned the Lord's table.
1-9: God condemns the priests for corrupt teaching that led people astray and contrasts them with the upright priests of the past. God warns them of judgement if they continue in their corrupt ways.
10-16: God rebuked Israel because many men in Judah married pagan women and were cut off from God's covenant because of it. God's second criticism was that they weren't faithful to their wives and divorced them.
17: God is wearied by those who claim He delights in evildoers. He is also wearied by those who accuse Him when He's silent during an injustice. Their implication is that God is unjust and will not deal with those who deserve judgement.
1-4: This prophesy may be referring to John the Baptist or Elijah. The Lord's coming described here is His second coming which will result in judgement. The purification of the priests could be referring to Jesus' atoning work that purifies them so their offerings will be accepted. This is not referring to offerings at the physical temple but offerings of obedience that are acceptable on the basis of Jesus' merits.
5:The second coming will be about justice for evil-doers.
6-7: God graciously withheld judgment by not destroying Israel despite their continual disobedience. This is due to His promise to Israel and His unchanging nature.
8-12: In the old covenant system blessing and cursing was directly related to Israel tithing. If they did not tithe they incurred cursing for robbing God by not giving back from everything He gave them. If they did tithe, he would bring them agricultural prosperity and the nations would take notice of God's blessing on them. This promise of blessing and cursing is clearly for Israel in an old covenant context and does not apply to believers today. We are no longer commanded to give one tenth of our resources and we are not Israel. However, the principle of giving back to God is repeated in the New Testament.
13-15: God rebuked Israel for speaking against him. They saw obedience to God as a pragmatic act to receive blessing. When they observed that those who reject God we're still blessed and prosperous they no longer saw a need to serve God. He was simply a means to an end for them.
16-18: Despite Israelis sins, there was a faithful remnant who feared and obeyed God. God promised to spare them on judgement day the way a father spares his son. Because Jesus died on their behalf they will be spared as if they were a Jesus himself. There will be a distinction between the righteous (those who have received Jesus' righteousness) and the wicked.
1-3: On the Day of the Lord the wicked will be judged. Malachi uses the imagery of burning trees to illustrate the devastation to come. Those who fear God and end up trusting in Jesus will be "healed" of their sin and be seen as guiltless on the day of judgement. The sun is a messianic metaphor for substitutionary atonement.
4: The law is important because it shows us a need for a savor, ultimately pointing us to Jesus
5-6: Luke 1:16 reveals the fulfillment of this prophecy is in John the Baptist, who came in the "spirit and power" of Elijah