The full context of the verse (with verse 10 highlighted in bold):
“For I, the Lord, do not change; therefore you, O sons of Jacob, are not consumed. From the days of your fathers you have turned aside from My statutes and have not kept them. Return to Me, and I will return to you,” says the Lord of hosts. “But you say, ‘How shall we return?’ Will a man rob God? Yet you are robbing Me! But you say, ‘How have we robbed You?’ In tithes and offerings. You are cursed with a curse, for you are robbing Me, the whole nation of you! Bring the whole tithe into the storehouse, so that there may be food in My house, and test Me now in this,” says the Lord of hosts, “if I will not open for you the windows of heaven and pour out for you a blessing until it overflows. Then I will rebuke the devourer for you, so that it will not destroy the fruits of the ground; nor will your vine in the field cast its grapes,” says the Lord of hosts. “All the nations will call you blessed, for you shall be a delightful land,” says the Lord of hosts. [Malachi 3:6-12]The book of Malachi details a series of criticisms against the nation of Israel (cf. Mal 1:1). It commonly features God making an accusation against the people about their transgressing His Law, followed by a presupposed objection the people might have (cf. Mal 1:6; 2:14; etc.), followed then by God's response and more detailed rebuke, along with an offer of reconciliation and a return to the blessings promised by the Law.
In this instance, God opens up by saying He, the Lord, does no change - meaning, in this context, that He does not change his mind regarding the covenant He made with Israel (v. 6). It is common for mortal man to give up on an agreement when the other person does not follow up with it, but it is not so with God. It is because of God's faithfulness to the covenant that He has not yet consumed the "sons of Jacob" (a reference to the promises made in Genesis 28:13 and 35:12) with judgment. These people rightly deserved judgment, because "from the days" of their fathers they "have turned aside" (that is, ignored) God's Law, and have not kept it (v. 7). However, the Lord asks them to return to Him (ie., repent), and He will return to them (ie., restore His blessings).
God then presupposes the question, "How shall we return?" In other words, what are the people to repent of, and how are they to repent? God accuses the people of robbery, and presupposes either their dumb ignorance or fake innocence with the question, "How have we robbed you?" The people are accused of not honoring the "tithes and offerings" (v. 8), but what are these "tithes and offerings"? In fact, these are references to the crops that were owed not only to the Temple (Lev 27:30-33), but which were provided for the Levites and priests (Num 18:8, 11, 19, 21-24), who had no land to sustain themselves like the other Jewish tribes had. The nation's failure to fulfill this obligation of the Law has placed them under a serious curse (v. 9).
Now we come to verse 10, where God commands the people to "bring the whole tithe into the storehouse." What does this mean? What is the "storehouse"? No doubt some pastors will attempt to spiritualize this to mean our bank accounts, but if we honor God by remaining true to the text of His holy word, we understand that this is speaking of the storehouse of the Temple (cf. Neh 13:5), as seen clearly by the following words "so that there may be food in My house." Remember, also, these are specific offerings God has commanded the people to give. These were the crops and produce of their land, and these were meant to go to the Temple (which no longer exists), and to support the Levitical priesthood (which has been replaced by Christ's priesthood). We cannot rip this verse out of it's context - we must adhere to what the word of God is saying.
Some might read God's command to "test" Him, and ponder if this is a contradiction with Deuteronomy 6:16, which clearly states not to test the Lord (and which was quoted by Christ against the devil). The key here is that these two verses actually have two different Hebrew words: Malachi 3:10 uses a form of bachan, which means to examine, try, or prove, and is often used in verses dealing with God testing mankind for their faith; Deuteronomy 6:16 uses a form of nasah, which means to test or tempt, and which, while often used in reference to God testing mankind, is also used in passages in which mankind puts God to the test, or in essence "tempts" Him to do something. Hence the KJV translation might be more accurate with the use of "prove" rather than "test."
Let me try to use an analogy to show how this verse is getting mishandled. Suppose I was good friends with someone at a car dealership, and he sold me a car for a good deal, with an understanding that I would meet the monthly payments to finish the rest of the cost. Some months down the road, I begin to fail to make the payments, and I get close to having my car repossessed...but, since we're friends, the car dealer gives me a friendly warning, saying, "You need to give me the money, and then you can keep the car." Now imagine if someone took the dealer's words and went around telling people, "Aha! Just throw money at the dealer, and he'll give you a car!" Is that an honest handling of the situation, and what the dealer said? Absolutely not.
On this note, those who attempt to use this verse to teach some kind of blessing for a monetary offering are actually in violation of Deuteronomy 6:16. When God says "put Me to the test" in Malachi 3:10, He is merely saying, "Act according to the statutes, and I will prove to you that I am faithful on my end of the covenant." On the other hand, those who teach that we should give as much as we can, as a way to see if God will do something in return, are, in essence, tempting God to act. They give as a way to say, "Come on, God, show me what You can do!" It is almost as if we are placing God under an obligation to give us financial blessing, when no such obligation exists.
Furthermore, if you continue on with the verse and those after it, you see that this blessing is agricultural in nature, not financial. It speaks of opening up "the windows of heaven," which is scriptural language for bringing rain (cf. Deu 28:12; Psa 78:23). He promises to rebuke "the devourer" (literally "the eater"), a reference to locusts and other insects which are destructive to crops; likewise, God will make certain the vineyards do not "cast" their grapes - literally "miscarry," and basically meaning a promise that the vineyards will bear fruit (v. 11). The reward will be so great that "all the nations" (meaning the Gentile nations) will call them blessed, for they are a "delightful man" (v. 12) - not meaning anything overtly spiritual, but simply meaning that, if Israel fulfills her end of the covenant, than the Gentile nations around them will see how happy and fulfilled they are.
No doubt, I'm sure, some preachers will here want to spiritualize all these things. The crops are our finances, the devourers are those who would take those finances from us (or maybe the devil, who takes time out of his day to try to make us poor), and the "nations" are those who can look at those in the church and see how prosperous Christians are. However, once again, this is robbing the passage of its original context, and spiritualizing it to say what we want it to say. We would not do this with any other historical document, and we would not want anyone doing this to our own words - why, then, should we treat the word of God with any less respect?
In conclusion, does Malachi 3:10 teach that, if we try to "out give" with our finances, we can test God and see what sort of blessings He will give us in return? On the contrary, it teaches nothing of the sort. Anyone who uses this passage to teach that it does is mishandling the word of God.