The short reason is because fiat currency is forbidden currency according to the Torah. So it is therefore a sin everyone is caused to be commit, by the mere possession, which is therefore what makes it the mark of the beast.
And the long reason is this,
And through the Federal Reserve Bank the USA brought a new form of money that would eventually be used by all central banks of the kingdoms of the earth that followed its example, “paper money”, for money before this time was gold and silver for thousands of years, which are rare enough and difficult enough to extract from the earth to make them valuable, which were minted in coins and used to buy and sell with them, which everyone in the world agreed was valuable and agreed to use to buy and sell, which is what “money” is, and the value of gold and silver was based on its weight, and each kingdom on the earth established their own name for a fixed measure of weight, such as “dollars”, “pesos”, “pounds”, and “shekels”, which were all previously names of weights, and the inhabitants of each kingdom bought and sold according to the number of those names of weights in gold, where 4 British Pounds of gold and 21 United States of America Dollars of gold and 21 Colombian Pesos of gold were equivalent to the weight of around 1 troy ounce of gold, yet in an evil financial scheme around 1933 AD the USA confiscated the gold of all Americans through an executive order it issued, and they were given certificates in exchange for the gold they were forced to give to the Federal Reserve Bank, and these certificates represented the gold they turned in and could also be used to redeem that same measure of gold they turned in, which were issued at a worth of around $21 USD per 1 troy ounce, and they could also be used to buy and sell as if it were money, “paper money”, for everyone agreed this paper money was valuable, not because the paper itself was valuable, but because they knew it represented gold at the bank, which they could redeem any time when banks were open, and then around 2 years later is when the thievery began, the Federal Reserve Bank devalued the paper money to around $35 USD per 1 troy ounce, thus stealing the gold Americans were forced to give to the Federal Reserve Bank in exchange for the certificates, and over several decades the Federal Reserve Bank continued stealing more by devaluing the paper money more and more, and by around this time all kingdoms of the earth were also adopting and issuing paper money through their own central banks to their own inhabitants, which today absolutely every kingdom on earth issues, even Cuba and North Korea, and then around 1971 AD is when the USA declared that paper money would no longer be redeemable in gold at a bank, which was a massive theft, because the banks kept all the gold that everyone was forced to give them while leaving everyone with mere paper money to continue buying and selling as if nothing happened, which is when paper money also became “fiat currency”, which is the worst form of debasement of money possible, because unlike the value of gold, which was based on its weight, the value of this form of money is now based on a “perceived imaginary” number given to it by those who issue it, for the paper money no longer represents the gold it was originally issued to represent, nor does it represent anything else of value in place of the gold, nor does the paper money represent the actual value of the paper itself, which has very little value, for it is common, so it is therefore a false value, a “perceived imaginary” value, a false weight, and a false number of a weight, and the mutual agreement of everyone to keep using paper money to buy and sell is what keeps it going, like a strong river that pushes anything in it and takes much strength to resist the strong flow of the river, and everyone is unaware that they have been deceived and robbed, very slowly, and continue to be robbed, very slowly, for those who issue paper money continue devaluing it more and more, as if stealing all that gold wasn’t enough, and as the incomes and salaries of the people lag behind the devaluation, then prices are caused to go up around them, which then causes them to go into debt with the same people that issue this form of money, and the debt is not given to them for free, it is given at interest, and thus, those who issued this form of money have not only became the owners of all the gold they stole for decades, but the owners of everything else in the world, through debt, houses through mortgages, cars through auto loans, possessions through credit cards, and many other forms of debt, thus leaving the world impoverished through paper money and fiat currency, and that is why today around 1,155 British Pounds and 1,500 United States Dollars and 164,000 Colombian Pesos buys the same 1 troy ounce of gold, it’s not that the value of gold has gone up, it’s that the value of paper money has gown down to epic proportions, and inhabitants of the world are not wealthier now, they are poorer, it is the greatest ponzi scheme of thievery the world has ever seen, which is the true explanation of the debt crisis in the USA, and although it may seem like Americans are wealthy and prosperous because they have houses and cars and possessions, most now have these things through debt, not making them true owners of anything, merely glorified slaves, an illusion of wealth, working daily to pay their debts to keep what they have or it will be taken away, and in other lesser nations, like Egypt for example, what they earn in minimum wage in 1 day in their fiat currency is sufficient enough to buy food for 1 day in a richer country like the USA, they are utterly impoverished through paper money and fiat currency, and in another example in Venezuela, their paper money and fiat currency has devalued so quickly that people there are eating food from garbage trucks, and few understand that the root cause of all these problems is the form of money itself, and even though the love of money was previously the root of all evil, now money itself has become the root of all evil, and therefore paper money and fiat currency is the true “mark of the beast”of Revelation, which is issued to everyone rich and poor and great and small in the world and promulgated unto the world through the second beast of Revelation, which is the USA, and is illegal to buy or sell without according to the law of legal tender, and because of the evil done through paper money and fiat currency is why the Torah forbids this form of money through commands that many think are irrelevant in our time, “you shall have righteous scales and stones” and “you shall not have in your bag one stone and another stone, a heavy and a light” and “you shall do no unrighteousness in judgment of measurements, weight, or volume”, and paper money and fiat currency is not a righteous and true value, because it was issued to represent gold and then was devalued and then became a false worthless value that no longer represented gold and then it is still continually devalued, “fiat currency”, an unrighteous and false value, which is far worst and more deceptive than thieves who existed thousands of years ago who had a heavier stone and a lighter stone of the same name of a weight in order to deceptively steal more gold putting the heavier version of the weight on a balance to make a sale, or putting a lighter version of the weight on the balance to deceptively give less gold when making a purchase, and through this form of money everyone is caused to commit sin, because the mere possession of false scales and false weights is already sin, meaning the mere possession of money is already sin, and it is not possessing gold and silver that is sin, for this is true money and acceptable to God in his Torah, but possessing this specific form of money that is sin, which is possessing paper money and fiat currency, and ultimately this form of money also only exists by the mutual consent of the people who use it daily to buy and sell, for if everyone agreed to exchange it for necessities and houses and gold and silver and stop receiving it and using it, this form of money would no longer exist, and the people would be left with what they need and gold and silver, while removing this financial system from their backs, which would then give rise to an economy using gold and silver to buy and sell like our ancestors did for thousands of years, which is good and true and valuable and stable money, because it cannot be devalued, for an 1 troy ounce of gold today is the same 1 troy ounce of gold tomorrow, whereas $100 USD today is not the same $100 USD tomorrow, and even though this is the intelligent way of how to remove this financial system from our backs, prophetically this is not destined to happen, because most people in the world would rather go with the flow of the river than resist the flow of the river, and even if the people did resist, it would perhaps not come without any sort of forceful or deadly intervention from those at the top of the hierarchy who have something to gain from the inhabitants of the earth continuing to use this financial system, and therefore, not possessing paper money and fiat currency is a true test of belief and obedience to those who truly love God versus those who truly love the world more than they love God, because not possessing this form of money cuts a person off from the entire whole wide world, and a person is left living like a poor person, even if he should have much gold, for no one or very few people in the world would accept it even to buy something as simple as a bottle of water, for the world has been deceived into believing this particular paper is money and not the gold that it was originally issued to represent, and in this way God has made money itself a stumbling block to the entire world, not just to test belief and obedience, but to give good reason to bring wrath and condemnation upon the entire world, for possessing paper money and fiat currency comes with the following curse, “whoever has taken the mark of the beast will be thrown into the lake of fire”.