3:1 “See, I will send My messenger [forerunner; see Mal. 4:5 re: Elijah; see Matt. 11:10 re: fulfillment in John the Baptist], who will prepare the way before Me. Then suddenly [unexpectedly] the Lord [Jesus Christ] you are seeking [even in their sin the people longed for deliverance through the Messiah] will come to His temple; the messenger of the covenant [only use of this phrase in OT], who you desire, will come [fulfilled in coming of Jesus],” says the Lord Almighty.
Note: Use of the pronoun “Me” establishes identification between the First and Second persons of the Trinity.
Christ came “to His temple” first as a baby to be dedicated, annually for festivals, and in the last week of His life.
3:2 But who can endure the day of His coming [cf. Amos 5:18-20]? Who can stand when He appears [to vindicate the righteous and punish the wicked]? For He will be like a refiner’s fire [eliminate impurities and refine; God’s refining fire morally transforms individuals] or a launderer’s soap [cleanses stains].
Note: Note that the first advent of Christ is pictured in 3:1 and His second coming in 3:2. “The day of His coming” or “Day of the Lord” refers to any day God steps into history to do a special work, whether judgment or deliverance.
3:3 He will sit [and wait for the fire to do its purifying work] as a refiner and purifier of silver; He will purify the Levites [see 3:1 re: “come to His temple”] and refine them [because they were responsible for the people’s spiritual decline; see 2:1-9] like gold and silver [see Matt. 23 re: Jesus’ words to religious leaders]. Then [after the refining process] the Lord will have men [righteous individuals] who will bring offerings in righteousness,
3:4 and the offerings of Judah and Jerusalem will be acceptable to the Lord, as in days gone by, as in former years [cf. 2:5-6; symbolic of cleansed/sanctified church].
Note: What impurities would God have to take out of your life to qualify you to bring offerings that are acceptable to the Lord? Remember: the heart of giving is the state of the heart.
3:5 “So I will come near to you for judgment. I [God] will be quick to testify [like a witness to a crime] against [activities condemned in the Law of Moses] sorcerers [perform witchcraft/magic], adulterers [violation of 7th Commandment] and perjurers [swear falsely; forbidden by 9th Commandment], against those who defraud laborers of their wages, who oppress the widows and the fatherless [those who are helpless and have no one to protect them], and deprive aliens of justice, but do not fear Me [cause for all the preceding sins; see Prov. 1:7],” says the Lord Almighty.
3:6 I the Lord do not change [immutability of God; contrary to the attitude expressed by the people in 2:17; see Heb. 13:8]. So you [as a result of God’s unchangeableness], O descendants of Jacob, are not destroyed [ended].
3:7 Ever since the time of your forefathers [past 900+ years] you have  turned away from My decrees and  have not kept them [terms of covenant]. Return [repent; people, not God, had broken the relationship] to Me, and I will return to you [indicates God’s willingness to receive His people],” says the Lord Almighty. “But you ask, ‘How are we to return? [attitude expressed is “Why do we need to return?” and suggests the people felt that they had never left God]‘
3:8 [because of sins listed in 3:5 and more specifically the specific sin listed here] “Will a man rob God [rhetorical question]? Yet you rob Me [evidence of why they needed to return to God]. “But you [people] ask, ‘How do we rob you?’ [God’s response] “In tithes [assigned to the Levites for their services as per Num. 18:21,24; see also Lev. 27:30-33] and offerings [voluntary contributions above the tithe].
Note: How much stealing takes place at your church on Sunday?
3:9 You are under a curse [see v. 11] — because you are robbing Me [God owns everything; Deut. 10:14; Ps. 24:1; Ps. 89:11].
3:10 [imperative] Bring the whole [no such thing as partial tithe] tithe into the storehouse [“house of supplies”], that there may be food [to support Levites, priests, temple workers; Levites depended on these gifts to feed their families since they had received no allotment of land; for poor and homeless — Deut. 14:28-29] in My house. Test Me in this,” says the Lord Almighty, “and see if I will not throw open the floodgates of heaven [see Gen. 7:11 re: “floodgates of heaven”] and pour out [probably a reference to rain; see mention of crops in vv. 11-12] so much blessing [not necessarily money; that which promotes your well-being] that you will not have room enough for it.
Note: In the Old Testament, tithes were to be taken to the place chosen by God (Deut. 12:11). Malachi challenged God’s people to bring their tithes into the storehouse (Mal. 3:10), a large chamber adjacent to the Temple (see Neh. 13:4-13). Respond to the following statement: Our commitment to God is reflected in our giving.
3:11 [see v. 9; see also Haggai 1:4-11] I will prevent pests [such as locusts, sometimes sent by God to devour crops as in Joel 2:25; can destroy an entire food supply overnight] from devouring your crops, and vines in your fields will not cast their fruit [see Matt. 6:33],” says the Lord Almighty.
3:12 “Then all the nations [those outside the covenant relationship with God] will [see God’s abundant blessings] call you blessed, for yours will be a delightful land,” says the Lord Almighty.
3:13 “You have said harsh things against me,” says the Lord. “Yet you ask, ‘What have we said against you?’
3:14 “You have said, ‘It is futile to serve God. What did we gain by carrying out his requirements and going about like mourners before the Lord Almighty?
3:15 But now we call the arrogant blessed. Certainly the evildoers prosper, and even those who challenge God escape.'”
3:16 Then those who feared the Lord talked with each other, and the Lord listened and heard. A scroll of remembrance was written in his presence concerning those who feared the Lord and honored his name.
3:17 “They will be mine,” says the Lord Almighty, “in the day when I make up my treasured possession. I will spare them, just as in compassion a man spares his son who serves him.
3:18 And you will again see he distinction between the righteous and the wicked, between those who serve God and those who do not.