The Hebrew word olam means in the far distance. When looking off in the far distance it is difficult to make out any details and what is beyond that horizon cannot be seen. This concept is the olam. The word olam is also used for time for the distant past or the distant future as a time that is difficult to know or perceive. This word is frequently translated as eternity or forever but in the English language it is misunderstood to mean a continual span of time that never ends. In the Hebrew mind it is simply what is at or beyond the horizon, a very distant time. A common phrase in the Hebrew is "l'olam va'ed" and is usually translated as "forever and ever" but in the Hebrew it means "to the distant horizon and again" meaning "a very distant time and even further" and is used to express the idea of a very ancient or future time.(1)
The Concept of Eternity.
The simple, basic truth is that Classical Hebrew, the Hebrew of the Old Testament Scriptures, has no term that carries the concept of "eternity." There are phrases that carry this concept, such as "without end," but there is not a single word that carries the concept of eternity as there is in English.
To focus on the meaning of the term for ever, here are some things to be kept in mind.
First, the Hebrew word is olam. The word itself simply means "long duration," "antiquity," "futurity," "until the end of a period of time." That period of time is determined by the context. Sometimes it is the length of a man's life, sometimes it is an age, and sometimes it is a dispensation.
The second thing to keep in mind is that there are two Hebrew forms of olam. The first form is le-olam, which means "unto an age." And the second form is ad-olam, which means "until an age." However, neither of these forms carry the English meaning of "forever." Although it has been translated that way in English, the Hebrew does not carry the concept of eternity as the English word "forever" does.
The third thing to keep in mind is that the word olam, le-olam, or ad-olam, sometimes means only up "to the end of a man's life." For example, it is used of someone's lifetime (Ex. 14:13), of a slave's life (Ex. 21:6; Lev. 25:46; Deut. 15:17), of Samuel's life (I Sam. 1:22; 2:35), of the lifetimes of David and Jonathan (I Sam. 20:23), and of David's lifetime (I Sam. 27:12; 28:2; I Chr. 28:4). While the English reads for ever, obviously from the context it does not mean "forever" in the sense of eternity, but only up to the end of the person's life.
The fourth thing to keep in mind about the meaning of olam is that it sometimes means only "an age" or "dispensation." For example, Deuteronomy 23:3 uses the term for ever but limits the term to only ten generations. Here it obviously carries the concept of an age. In 2 Chronicles 7:16, it is used only for the period of the First Temple. So, again, the word for ever in Hebrew does not mean "eternal" as it does in English; it means up to the end of a period of time, either a man's life, or an age, or a dispensation.(2)
Concerning a law in the Talmud that prohibits trying to come up with a date of the coming of the Messiah, one of the greatest Jewish commentators of all time, Maimonides (Rambam) wrote this:
Rambam, after citing the Talmudic injunction in his code and elaborating on it in his "Igeret Teyman" himself offers in the latter (ch.3) a date passed on to him by his ancestors! Rambam confronts the problem by stating that the Talmudic prohibition was but for a limited time only and no longer applies to the present era of "Ikvot Meshicha."(3)
For more proof that the writers of the Talmud knew that the Mosaic Law would not last forever please read Talmud Comments On Mosaic Law:
For a more in depth reading on this issue please see http://hadavar.org/lawofmoses.html
3). Mashiach, The Principle of Mashiach and the Messianic Era in Jewish Law and Tradition by Jacob Immanuel Schochet (New Expanded Edition) p.43.