In Hebrews 7, it becomes clear that Melchizedec is a priest that was tithed to, and that Jesus Himself was high priest according to the order of Melchizedec. So then, his priesthood of believers, being priests according to the order of Melchizedec, can receive the tithe.
So by example, the tithe to Melchizidek was singular, and never repeated, and it was only from the spoils of war. It does not establish a perpetual obligation or blessing.
Receiving the blessing of Malachi 3:10 has nothing to do with giving by on. You give your 10% with the understanding that He will pour out for you a blessing; but you do not give because you feel that you have to: you give because you know there is a blessing in it.
The tithe in the Old Covenant was essentially what we would call an income tax. It only applied to increase received from the fruit of the earth/agriculture. The arrangement was that the Priesthood would be supported by this tax. This was no voluntary tax. They were in a drought, and the farmers were not giving what they were supposed to. The Priests were suffering or possibly starving. God promises to break the drought if the obeyed and brought in what was compulsory for them to do.
The "blessing" or "promise" was opening the windows of heaven... Rain! (And rain would water the crops and they would be blessed.)
So, unless you gain the spoils of war, or are a farmer, neither of these passages can possibly be applied to giving a tenth of your income that is acquired in any way apart from what is stated.
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