Why does the Rabbi have certain suspicions about this? Is it possible that this is not from the Torah given at Sinai?

The question is whether this was said as a practical instruction to test the Holy One, blessed be He, and when it is supposed to work and how the test is supposed to be carried out. And maybe it was said only for encouragement and rhetorical flourish (“don’t worry about the loss”), and not as a practical instruction.

Hello Rabbi,
If it was said only as encouragement, then why is there a binding ruling in the Shulchan Arukh, Yoreh De'ah, requiring one to give tithes?

With God’s help, 15 Elul 5777, the New Year for the animal tithe

To Israel — greetings,

If the prophet promises, then it certainly works; but like any experiment, one has to be careful about the conditions. For example: (a) setting aside the tithe exactly. (b) making sure it is given for proper purposes according to Jewish law. (c) not doing things that naturally lead to poverty, such as financially irresponsible conduct or committing sins that lead to poverty.

It is worth noting that beyond the prophet’s promise, the very act of setting aside the tithe is also a natural recipe for success. It trains a person to live according to a budget and to pay attention to income and expenses. It also trains him not to spend everything immediately, but to put money aside for times of need. Rabbi Eliezer Melamed suggests setting aside from every income one tenth for charity and one tenth for savings.

Moreover, when a person sees how much blessing the tenth he gave brought to those in need, and how much they thank him for the little he gave them, he suddenly discovers how great the value is of the other nine tenths left in his hands, and he is happy with his lot.

When a person helps himself, manages his affairs wisely, and conducts business faithfully, then the blessing of God comes, preserving and developing things, and completing the natural human effort. That is how it seems to me, in my humble opinion.

On the subject of tithing money: Is it a Torah-level obligation, a rabbinic one, or a custom? And is one obligated in it even when one’s financial situation is tight? And was the prophet’s promise, “Test Me,” said only about the agricultural tithe (which is what the verse is discussing), or also about “tithing money”? And for what purposes may one use tithe money, etc.? See Rabbi Eliezer Melamed’s lesson, “Charity and Tithing Money,” on the Yeshiva website. “Give to a wise man and he will become wiser still.”

With blessings,
S. Z. Levinger

Israel, I didn’t understand your question. The obligation of tithing is written as an obligation. What we were discussing was only the promise of “Test Me now with this.”