That was their money back then. They gave to the Lord from what they had in their possessions before money was instituted. God demanded a tenth.
Are you joking? Not only was the tithe not money, but it wasn't income.
The Bible shows they not only had money, but that money was used as a common way of doing business.
According to the International Bible Encyclopedia, the days of mere bartering ended before the days of Abraham.
Here are just a few examples from The Word to show they did, in fact, use money in Biblical times.
The tithing law itself proves they had both money and a marketing system for buying and selling their crops and animals (Deuteronomy 14:24-26).
THE PURCHASE OF LAND WITH MONEY BY ABRAHAM - Genesis 23:15-16
THE PURCHASE OF LAND WITH MONEY BY JACOB - Genesis 33:19
JOSEPH WAS SOLD TO THE ISHMEELITES FOR MONEY - Genesis 37:28
A MONEY OFFERING TO BE USED FOR THE SERVICE OF THE TABERNACLE - Exodus 30:14-16,
USING SHEKEL OF SILVER TO VALUE A RAM - Leviticus 5:15
THE FOLLOWING VERSES REFER TO WAGES: Genesis 29:15, Genesis 30:28, Genesis 31:7-8, Genesis 31:41, Exodus 2:9, Leviticus 19:13, Malachi 3:5, etc.
THEY HAD A MONEY STANDARD
There are several places in Scripture indicating that scales were used to weigh metals and other items. The Law of Moses, for example, commands Jews not to use dishonest standards, but instead, to use honest scales and honest weights. (See also Deut. 25:13-15; Job 6:2-3; 31:6; Psa. 62:9; Prov. 11:1; 16:11; 20:10, 23; Isa. 40:12; 46:6; and Jer. 32:10).
Leviticus 19:35-36 Do not use dishonest standards when measuring length, weight or quantity. Use honest scales and honest weights, an honest ephah and an honest hin. I am the LORD your God, who brought you out of Egypt.
In order for money to be an exchangeable equivalent for other commodities in todays society, there must be a standard in place. Likewise, the Old Testament also had a set standard both prior to the law and during the law. A reference to a pre-law standard is in Genesis 23:16.
Merchants in biblical times traveled from place to place conducting business. According to the written law, the standard weight for metals was set according to the sanctuary shekel (See also Ex 30:13, 24; 38:24-26; Lev. 5:15; Num. 7:13-86; 18:16).
Leviticus 27:25 Every value is to be set according to the sanctuary shekel,
In addition, 2 Samuel 14:26 shows that the weight standard for the shekel was set by the royal standard. No matter which era in history is studied, there existed a standard for the weight of precious metals.
Money was also used throughout the law. For example, Gods people gave money to support the tabernacle (Ex. 30:14-16; 38:24-31). There are many other examples that illustrate moneys place within the written law and indicate that money was indeed a part of everyday life. Exodus 35 provides such an example.
Exodus 35:5, 21-22 From what you have, take an offering for the LORD. Everyone who is willing is to bring to the LORD an offering of gold, silver and bronze;
And there are many more examples to show that money was used for everyday transactions well before the Levitical tithe.