It is my understanding that restrictions and prohibitions on the Sabbath more accurately concern "creating" or "destroying" rather than the stereotypical concept of "working". Why is it then acceptable to have relations since such is an act of "creating"? In fact, if I understand correctly, husband and wife relations on the Sabbath is considered a mitzvah. Thank you for your response (s).
On Shabbat, one is not prohibited from doing all creative work, only that which fall into one of the 39 Categories. These categories were determined based on the creative work necessary for the construction of the Mishkan (Tabernacle), and since procreation was not necessary for the construction, it is not prohibited.
In addition, it is unclear if sexual relations are an act of creation. It is not guaranteed the relations on Shabbat will lead to a conception, and even if it did, the rabbis held that an embryo isn't viable until 40 days after conception.
Regarding the Mitzvah aspect:
The Babylonian Talmud (Ketubot 62b) elaborates that the designated time for scholars to engage in physical intimacy with their wives is Friday night:
How often are scholars to perform their marital duties? Rav Judah in the name of Samuel replied: “Every Friday night…” Judah the son of R. Hiyya and son-in-law of R. Jannai would spend all his time in the schoolhouse but every Sabbath eve he came home.
This was codified by the Shulchan Aruch (Orach Chaim 280:1)
תשמיש המטה מתענוגי שבת הוא, לפיכך עונת תלמידי חכמים הבריאים מליל שבת לליל שבת.
Marital relations are among the delights ("oneg") of Shabbat, and therefore the time for marital relations for a healthy Torah scholar is from Friday night to Friday night.
Additional information can be found at: http://www.thejc.com/judaism/rabbi-i-have-a-problem/68658/why-sex-allowed-shabbat
There is an interesting article at http://thetorah.com/intimacy-on-shabbat which explains that some Second Temple sects believed sex to be prohibited on Shabbat.
Jubilees, a book dated to the 2nd century BCE and found among the Dead Sea Scroll documents, expresses the divine commandment to observe the Sabbath in the following manner:
Six days you will work, but the seventh day is the Sabbath of the LORD your God… And let the man who does anything on it die. Every man who will profane this day, who will lie with his wife… let him die.
Rather astonishingly, Jubilees posits that sexual intercourse on Sabbath is punishable by death.
As Shmuel wrote, relations does not involve any of the 39 forbidden activities and is not forbidden.
I would like to add a few additional thoughts:
- Any act of creation in zygote formation takes place at the microscopic level which, in general, is not viewed halachically as a significant action.
- Zygote creation takes place within the context of marital relations and is not forbidden. We find that although one may not squeeze grapes as it violates the melacha of dosh ( sechita ), nevertheless one may eat and chew grapes on Shabbos and even deliberately crush grapes in his mouth (Orach Chaim 320:1, Mishne Berurah 12) beacuse it is viewed as an act of eating. Similarly, relations by itself is permitted and any possible resultant "creation" is viewed as done within the context of marital relations and is not creation.