Wonderfully God does not change and therefore is completely faithful to his covenant promises and sticks by his choice of Jacob (cf.1:2,3). He is unchangeably loving and gracious and merciful. Were it not so they would be destroyed, for they too sadly have not changed but have been persistently faithless to the covenant. They are very much sons of Jacob, their devious and grasping and faithless ancestor.
For them to return is to repent; for God to return is to bless them again. Their question implies that they don’t see anything they need to repent of.
God has already put his finger on a number of very practical areas of disobedience – their marriages, their attitude to church (as we might put it) – and now God addresses their giving. Not that they didn’t give, but they failed to bring in the whole tithe (v.10). Back in chapter one it was the quality of their offerings that was criticised, here it is the quantity. By withholding what belonged to God they were robbing him.
The tithes were used to feed the priests in the temple, and if they were not properly provided for this would have a knock-on effect on their willingness to perform their temple duties (cf.1:6-2:9).
Money is the issue here, but it might be worth noting that we rob from God whenever we withhold from him what is rightfully his; it may be quite a different area of our life in which we are tempted to say to God – “You can’t have that! It’s mine!”
God will never be out-given. “Test me,” he says. His curse has afflicted them in the very area of their disobedience – their harvests – and the blessing that would follow their obedience would be in the same area: they would know abundance and protection from loss.
Verse 12 suggests that God longs to bless his people not least so that his name might be great among the nations (cf. 1:11).
This passage obviously raises questions about tithing today (though, as mentioned above, application of these verses needn’t be restricted to giving). The New Testament gives no indication that we are still under the laws to do with tithing, but being under grace should mean if anything a greater willingness to be generous in our giving. And the NT is clear that our attitude to our money can still be a very significant indicator of the state of our relationship with God – of how we view him, and how we view our money.
The way we might expect God to know God’s blessing now is not primarily materially either (contra the teaching of the prosperity gospel). But there is a blessing we can expect as we are obedient in the area of giving, and it may in part be material (cf. 2 Cor.8:6-15.) Certainly, as we put our lives in God’s hands (including our finances) we will find that he does indeed take care of us. Withholding the tithe was an expression of self-dependence and self-sufficiency – and that is the way of curse and not blessing, it is the way of going it alone, rather than of walking with God.