It is precisely because it is believed that only the Jerusalem Temple is endowed with essential, or intrinsic, holiness, while synagogues are seen as no more than temporary places in which Jews can assemble for prayer and whose sanctity is entirely utilitarian, that there are only the barest of regulations governing the synagogue architecture and aesthetics. The cardinal rule regarding synagogue aesthetics is the complete ban on the presence of any images, or icons, of either God or humans. Judaism's rigid iconoclasticism can be traced back to the second of the Ten Commandments, which prohibits the creation and worship of any "graven images." This stylistic openness, combined with the worldwide dispersal of the Jewish Diaspora, has resulted in a plethora of architectural styles, most often greatly influenced by the prevailing trends in the surrounding gentile communities. It was not until the rise of the grand Reform Temples in early 19th-century Europe that Jewish houses of worship were obviously designed to emulate the style of Christian Churches, both externally and internally.
Despite this lack of architectural uniformity, all traditional synagogues contain several essential features. The most important and sacred of these is the Aron ha-kodesh, or Holy Ark, that contains the congregation's Torah (parchment scrolls on which the traditional Hebrew, or Masoretic, text of the Pentateuch, or Five Books of Moses, have been inscribed by a specially trained religious calligrapher known as a sofer, or scribe). The Torah scroll is Judaism's supremely sacred religious object and is treated with great veneration. The Holy Ark is covered with a curtain, which when opened during the course of religious services, signals the entire congregation to rise out of deference to the Torah. When the Torah scrolls are removed from the ark for their public reading, members of the congregation customarily rush forward to bow before, or kiss, them.
In addition to the Aron ha-kodesh, modeled after the Holy Ark at the center of the Holy of Holies in the ancient Israelites' desert sanctuary and later in the Jerusalem Temple, and the amud, from which the cantor leads the services, traditional synagogues all feature a central, elevated stage, known as the bimah. The bimah serves primarily as the platform from which the Torah is read, although in many congregations the cantor leads the major Shabbat and festival services from it as well. In the modern period, Reform Temples replaced the central bimah with an altar in the front of the synagogue, from which the cantor chanted services facing the congregation. Aside from the gender-integrated seating, this was among the most controversial changes to synagogue architecture initiated by the Reform movement. The other was the introduction of pipe-organs and choral lofts, all in emulation of the aesthetics of European churches.
Synagogues are required to maintain an "eternal light," a lamp or lantern that typically hangs from the ceiling just above and in front of the Aron ha-kodesh. This ritual object, like many others in the rabbinic tradition, is purely commemorative, symbolizing the eternal light of the seven-pronged candelabra kindled daily by the Israelite priests in the Jerusalem Temple.