It is important to make note of verse 31:13 in the Book of Shemot. This is the source for the thirty-nine Melachot of Shabbat. This is learned from the words, אך את שבתתי תשמורו, “But you shall observe my Sabbaths.”
The positioning of this Pasuk right in the middle of the numerous chapters, discussing the construction of the Tabernacle, is significant. Those thirty-nine activities forbidden on Shabbat, were activities that were done as part of the construction.
It is also interesting to emphasize that in order to have violated any of these Melachot, they must be done in the same manner it was done in the desert. In order to save an individual of a Torah violation, there is the concept of כלאחר יד, that literally means, “the back of the hand.”
If, for example, one carries an object from a private to a public domain on his shoe, it would be a rabbinic violation and not a Torah violation. This exemption should only be done, in time of need. It should not be done routinely.
Some ignorantly believe that it’s perfectly okay to turn on a light with one’s elbow. This is כלאחר יד, and does reduce the infraction to rabbinic. However, a rabbinic violation must not be taken lightly. The Oral Law is based on the teachings of the Rabbis, and must be observed. The כלאחר יד exemption should only be done בשעת הדחק, under exceptional circumstances. It must not be abused or belittled.
Shabbat laws are very intricate and detailed. One must study and cherish them, for Shabbat is one of the greatest gifts given to the Jewish people.