Tosefos and Sifri1 quote the verse: "You shall tithe all the produce of your seed which the
field yields year by year," and ask: " 'You shall tithe all the produce of your seed' only indicates that
ma'aser is to be given from one's produce. How do we know that it is necessary to give
ma'aser from other things?"
They answer: "We know this from the word 'all.' The verse could have simply stated: 'You
shall tithe the produce of your field.' The extra word 'all' comes to teach us that ma'aser is to be
given from all of one's earnings."
The [above-mentioned verse concludes with the] words, "which the field yields year by
year." When a person gives ma'aser , G-d blesses that from which ma'aser was given.
However, when ma'aser is not given, then a field will only produce the amount that should have been
given as ma'aser during the previous year. "Which the field yields year by year" thus means to say
that the amount a field yields in one year depends on the amount of ma'aser given during the
previous year.
There once was an individual2 who scrupulously observed the mitzvah of ma'aser. This person
had a field that yielded one thousand measures of grain annually, one hundred of which he would give for
ma'aser. He conducted himself in this fashion all his life, and was very wealthy. Before his death
he called his son and said to him: "This particular field yields one thousand measures of grain annually." He
further told his son that he should be sure to give one hundred measures for ma'aser each year.
The first year after his father's passing the son gave the one hundred measures. The
following year, however, he decided that one hundred measures was too much, and gave no ma'aser at
all.
The following year his field produced only one hundred measures of grain.
His relatives said to him: "When you conducted yourself in the manner your father
commanded, the field gave one thousand measures of grain and you gave one hundred of them for
ma'aser. At that time you were the owner and G-d was the Kohain, the priestly recipient.
However, when you decided not to give ma'aser, only one hundred measures of grain grew, for then G-d
was the owner, and you were the priestly recipient."
This is also implied by the verse: "The sacred offerings of each individual remain his
property."3 In other words,
the manner in which a person conducts himself with regard to his "sacred offerings" [his gifts of
ma'aser and the like], affect his property. He who does not give ma'aser properly is left
with only the amount he should have given. He that gives ma'aser unstintingly receives a multitude
of blessings. This is why G-d blessed Yitzchok; Yitzchok's giving of ma'aser resulted in his
becoming exceedingly wealthy.
In summary: Ma'aser is to be given from all of one's possessions. A wondrous
story is told concerning ma'aser. Ma'aser is given by a landowner to a priest. When
ma'aser is given, the person is the landowner and G-d is the priest. When ma'aser is not given,
G-d becomes the landowner and the person becomes the priest, who receives only a tenth of what he would have
had if he had given ma'aser.