The Torah commands us to contribute a Machatzis HaShekel, a half shekel, towards the construction of the Mishkan. The Gemara in Kiddushin 40b states that one should always view the world as if it is hanging in the balance, with half the world innocent and half the world guilty. If one performs a mitzvah, he tips the scales towards the side of merit, and if heaven forbid he commits a transgression, then the scales are tipped towards the side of liability. This idea is alluded to in the words Machatzis HaShekel, as the word Machatzis means half, and the word shekel is similar to the word mishkal, which means weights, i.e. scales of judgment. One should always view the world as if it is hanging in the balance, i.e. half meritorious and half liable, and his actions can determine which way the scales of judgment will tip. On a different note, the Torah states esrim gerah HaShekel, the shekel is twenty geras. This can be interpreted in the following manner. Regarding the verse that states aser teaser, you shall tithe, the Gemara in Taanis 9a states that the verse can be interpreted to mean aser, give tithes, bishvil shetisaser, in order that you become wealthy. Similarly, we can suggest that the verse in Ki Sisa means esrim, give Maaser, tithes; gerah, which is from the root word of gorer, to be drawn after. Give Maaser so that gerah HaShekel, your act of giving Maaser will lead to shekel, becoming wealthy.