"And they shall make a Temple for Me, and I will dwell among them..." [25:8]
In the (Medrash) Pesikta, it says that when G-d said this, Moshe trembled.
"How is it possible to build a house for G-d, who encompasses and
transcends all the heavens?" And G-d replied, "not by my standards, but in
accordance with their abilities: twenty boards in the North..."
Then when G-d began to discuss the sacrifices, Moshe said, "would all the
animals in the world provide even a single fitting sacrifice?" And G-d
replied, "not like your thinking, but a single sheep in the morning..." And
when G-d began to discuss the annual gift to the Temple, "each person in
redemption for his soul," Moshe again said "how could a person ever give
enough to redeem himself?" And once again, G-d replied, "not like your
thinking, but one-half Shekel according to the sanctified Shekel measure..."
The Chofetz Chaim learns from this Medrash that G-d does not make
impossible demands upon us. Every person is obligated to do only that which
he or she can. As King Solomon said in Kohelet (Ecclesiastes) 9:10, "All
that you find within your ability to do, act upon it..." which is to say,
only that which is within your ability. We must do only that which has been
placed upon us.
Every person is obligated to study, but according to one's abilities -- be
that Mishna, Talmud, or Codes of Law. Similarly, a person is obligated to
give charity according to his or her wealth. A wealthy person cannot give
only the amount expected of a poor person, and claim to have fulfilled his
or her obligation, but neither should a poor person give away everything
trying to meet the standards of the rich.
A person must not become discouraged, worrying that it is impossible to do
everything -- and then do nothing. On the contrary: we must do everything
that we can!